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Auto merge of #119722 - matthiaskrgr:rollup-y6w3c9h, r=matthiaskrgr
Rollup of 5 pull requests Successful merges: - #116129 (Rewrite `pin` module documentation to clarify usage and invariants) - #119703 (Impl trait diagnostic tweaks) - #119705 (Support `~const` in associated functions in trait impls) - #119708 (Unions are not `PointerLike`) - #119711 (Delete unused makefile in tests/ui) r? `@ghost` `@rustbot` modify labels: rollup
This commit is contained in:
bors
@@ -106,7 +106,8 @@ ast_lowering_misplaced_double_dot =
|
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.note = only allowed in tuple, tuple struct, and slice patterns
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ast_lowering_misplaced_impl_trait =
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`impl Trait` only allowed in function and inherent method argument and return types, not in {$position}
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`impl Trait` is not allowed in {$position}
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.note = `impl Trait` is only allowed in arguments and return types of functions and methods
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ast_lowering_misplaced_relax_trait_bound =
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`?Trait` bounds are only permitted at the point where a type parameter is declared
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@@ -90,6 +90,7 @@ pub enum AssocTyParenthesesSub {
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#[derive(Diagnostic)]
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#[diag(ast_lowering_misplaced_impl_trait, code = "E0562")]
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#[note]
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pub struct MisplacedImplTrait<'a> {
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#[primary_span]
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pub span: Span,
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@@ -12,6 +12,7 @@
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use rustc_hir::def_id::{LocalDefId, CRATE_DEF_ID};
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use rustc_hir::PredicateOrigin;
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use rustc_index::{Idx, IndexSlice, IndexVec};
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use rustc_middle::span_bug;
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use rustc_middle::ty::{ResolverAstLowering, TyCtxt};
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use rustc_span::edit_distance::find_best_match_for_name;
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use rustc_span::symbol::{kw, sym, Ident};
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@@ -182,7 +183,8 @@ fn lower_item_kind(
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self.lower_use_tree(use_tree, &prefix, id, vis_span, ident, attrs)
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}
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ItemKind::Static(box ast::StaticItem { ty: t, mutability: m, expr: e }) => {
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let (ty, body_id) = self.lower_const_item(t, span, e.as_deref());
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let (ty, body_id) =
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self.lower_const_item(t, span, e.as_deref(), ImplTraitPosition::StaticTy);
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hir::ItemKind::Static(ty, *m, body_id)
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}
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ItemKind::Const(box ast::ConstItem { generics, ty, expr, .. }) => {
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@@ -191,7 +193,9 @@ fn lower_item_kind(
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Const::No,
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id,
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&ImplTraitContext::Disallowed(ImplTraitPosition::Generic),
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|this| this.lower_const_item(ty, span, expr.as_deref()),
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|this| {
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this.lower_const_item(ty, span, expr.as_deref(), ImplTraitPosition::ConstTy)
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},
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);
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hir::ItemKind::Const(ty, generics, body_id)
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}
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@@ -448,8 +452,9 @@ fn lower_const_item(
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ty: &Ty,
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span: Span,
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body: Option<&Expr>,
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impl_trait_position: ImplTraitPosition,
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) -> (&'hir hir::Ty<'hir>, hir::BodyId) {
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let ty = self.lower_ty(ty, &ImplTraitContext::Disallowed(ImplTraitPosition::ConstTy));
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let ty = self.lower_ty(ty, &ImplTraitContext::Disallowed(impl_trait_position));
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(ty, self.lower_const_body(span, body))
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}
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@@ -572,23 +577,25 @@ fn lower_assoc_item(
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// This is used to track which lifetimes have already been defined,
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// and which need to be replicated when lowering an async fn.
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match parent_hir.node().expect_item().kind {
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let generics = match parent_hir.node().expect_item().kind {
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hir::ItemKind::Impl(impl_) => {
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self.is_in_trait_impl = impl_.of_trait.is_some();
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&impl_.generics
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}
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hir::ItemKind::Trait(_, _, generics, _, _) if self.tcx.features().effects => {
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self.host_param_id = generics
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.params
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.iter()
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.find(|param| {
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matches!(
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param.kind,
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hir::GenericParamKind::Const { is_host_effect: true, .. }
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)
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})
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.map(|param| param.def_id);
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hir::ItemKind::Trait(_, _, generics, _, _) => generics,
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kind => {
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span_bug!(item.span, "assoc item has unexpected kind of parent: {}", kind.descr())
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}
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_ => {}
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};
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if self.tcx.features().effects {
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self.host_param_id = generics
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.params
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.iter()
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.find(|param| {
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matches!(param.kind, hir::GenericParamKind::Const { is_host_effect: true, .. })
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})
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.map(|param| param.def_id);
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}
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match ctxt {
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@@ -304,8 +304,6 @@ enum ImplTraitPosition {
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ClosureParam,
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PointerParam,
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FnTraitParam,
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TraitParam,
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ImplParam,
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ExternFnReturn,
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ClosureReturn,
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PointerReturn,
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@@ -324,29 +322,27 @@ impl std::fmt::Display for ImplTraitPosition {
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fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
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let name = match self {
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ImplTraitPosition::Path => "paths",
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ImplTraitPosition::Variable => "variable bindings",
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ImplTraitPosition::Variable => "the type of variable bindings",
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ImplTraitPosition::Trait => "traits",
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ImplTraitPosition::AsyncBlock => "async blocks",
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ImplTraitPosition::Bound => "bounds",
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ImplTraitPosition::Generic => "generics",
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ImplTraitPosition::ExternFnParam => "`extern fn` params",
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ImplTraitPosition::ClosureParam => "closure params",
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ImplTraitPosition::PointerParam => "`fn` pointer params",
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ImplTraitPosition::FnTraitParam => "`Fn` trait params",
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ImplTraitPosition::TraitParam => "trait method params",
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ImplTraitPosition::ImplParam => "`impl` method params",
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ImplTraitPosition::ExternFnParam => "`extern fn` parameters",
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ImplTraitPosition::ClosureParam => "closure parameters",
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ImplTraitPosition::PointerParam => "`fn` pointer parameters",
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ImplTraitPosition::FnTraitParam => "the parameters of `Fn` trait bounds",
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ImplTraitPosition::ExternFnReturn => "`extern fn` return types",
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ImplTraitPosition::ClosureReturn => "closure return types",
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ImplTraitPosition::PointerReturn => "`fn` pointer return types",
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ImplTraitPosition::FnTraitReturn => "`Fn` trait return types",
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ImplTraitPosition::FnTraitReturn => "the return type of `Fn` trait bounds",
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ImplTraitPosition::GenericDefault => "generic parameter defaults",
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ImplTraitPosition::ConstTy => "const types",
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ImplTraitPosition::StaticTy => "static types",
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ImplTraitPosition::AssocTy => "associated types",
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ImplTraitPosition::FieldTy => "field types",
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ImplTraitPosition::Cast => "cast types",
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ImplTraitPosition::Cast => "cast expression types",
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ImplTraitPosition::ImplSelf => "impl headers",
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ImplTraitPosition::OffsetOf => "`offset_of!` params",
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ImplTraitPosition::OffsetOf => "`offset_of!` parameters",
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};
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write!(f, "{name}")
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@@ -364,19 +360,6 @@ enum FnDeclKind {
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Impl,
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}
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impl FnDeclKind {
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fn param_impl_trait_allowed(&self) -> bool {
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matches!(self, FnDeclKind::Fn | FnDeclKind::Inherent | FnDeclKind::Impl | FnDeclKind::Trait)
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}
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fn return_impl_trait_allowed(&self) -> bool {
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match self {
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FnDeclKind::Fn | FnDeclKind::Inherent | FnDeclKind::Impl | FnDeclKind::Trait => true,
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_ => false,
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}
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}
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||||
}
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#[derive(Copy, Clone)]
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enum AstOwner<'a> {
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NonOwner,
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@@ -1842,19 +1825,19 @@ fn lower_fn_decl(
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inputs = &inputs[..inputs.len() - 1];
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}
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let inputs = self.arena.alloc_from_iter(inputs.iter().map(|param| {
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let itctx = if kind.param_impl_trait_allowed() {
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ImplTraitContext::Universal
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} else {
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ImplTraitContext::Disallowed(match kind {
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FnDeclKind::Fn | FnDeclKind::Inherent => {
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unreachable!("fn should allow APIT")
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}
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FnDeclKind::ExternFn => ImplTraitPosition::ExternFnParam,
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FnDeclKind::Closure => ImplTraitPosition::ClosureParam,
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FnDeclKind::Pointer => ImplTraitPosition::PointerParam,
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FnDeclKind::Trait => ImplTraitPosition::TraitParam,
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FnDeclKind::Impl => ImplTraitPosition::ImplParam,
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})
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let itctx = match kind {
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FnDeclKind::Fn | FnDeclKind::Inherent | FnDeclKind::Impl | FnDeclKind::Trait => {
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ImplTraitContext::Universal
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}
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FnDeclKind::ExternFn => {
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ImplTraitContext::Disallowed(ImplTraitPosition::ExternFnParam)
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}
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FnDeclKind::Closure => {
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ImplTraitContext::Disallowed(ImplTraitPosition::ClosureParam)
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}
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FnDeclKind::Pointer => {
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ImplTraitContext::Disallowed(ImplTraitPosition::PointerParam)
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}
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};
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self.lower_ty_direct(¶m.ty, &itctx)
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}));
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@@ -1866,26 +1849,25 @@ fn lower_fn_decl(
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}
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None => match &decl.output {
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FnRetTy::Ty(ty) => {
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let context = if kind.return_impl_trait_allowed() {
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let fn_def_id = self.local_def_id(fn_node_id);
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ImplTraitContext::ReturnPositionOpaqueTy {
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origin: hir::OpaqueTyOrigin::FnReturn(fn_def_id),
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let itctx = match kind {
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FnDeclKind::Fn
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| FnDeclKind::Inherent
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| FnDeclKind::Trait
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| FnDeclKind::Impl => ImplTraitContext::ReturnPositionOpaqueTy {
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origin: hir::OpaqueTyOrigin::FnReturn(self.local_def_id(fn_node_id)),
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fn_kind: kind,
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},
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FnDeclKind::ExternFn => {
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ImplTraitContext::Disallowed(ImplTraitPosition::ExternFnReturn)
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}
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FnDeclKind::Closure => {
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ImplTraitContext::Disallowed(ImplTraitPosition::ClosureReturn)
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}
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FnDeclKind::Pointer => {
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ImplTraitContext::Disallowed(ImplTraitPosition::PointerReturn)
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}
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} else {
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ImplTraitContext::Disallowed(match kind {
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FnDeclKind::Fn
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| FnDeclKind::Inherent
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| FnDeclKind::Trait
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| FnDeclKind::Impl => {
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unreachable!("fn should allow return-position impl trait in traits")
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}
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FnDeclKind::ExternFn => ImplTraitPosition::ExternFnReturn,
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FnDeclKind::Closure => ImplTraitPosition::ClosureReturn,
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FnDeclKind::Pointer => ImplTraitPosition::PointerReturn,
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})
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};
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hir::FnRetTy::Return(self.lower_ty(ty, &context))
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hir::FnRetTy::Return(self.lower_ty(ty, &itctx))
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}
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FnRetTy::Default(span) => hir::FnRetTy::DefaultReturn(self.lower_span(*span)),
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},
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@@ -120,11 +120,11 @@ pub fn unadjusted_abi_align(self) -> Align {
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/// Whether the layout is from a type that implements [`std::marker::PointerLike`].
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///
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/// Currently, that means that the type is pointer-sized, pointer-aligned,
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/// and has a scalar ABI.
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/// and has a initialized (non-union), scalar ABI.
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pub fn is_pointer_like(self, data_layout: &TargetDataLayout) -> bool {
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self.size() == data_layout.pointer_size
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&& self.align().abi == data_layout.pointer_align.abi
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&& matches!(self.abi(), Abi::Scalar(..))
|
||||
&& matches!(self.abi(), Abi::Scalar(Scalar::Initialized { .. }))
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||||
}
|
||||
}
|
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|
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|
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+42
-19
@@ -899,25 +899,37 @@ impl<T: ?Sized> !Freeze for UnsafeCell<T> {}
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{T: ?Sized} &mut T,
|
||||
}
|
||||
|
||||
/// Types that can be safely moved after being pinned.
|
||||
/// Types that do not require any pinning guarantees.
|
||||
///
|
||||
/// Rust itself has no notion of immovable types, and considers moves (e.g.,
|
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/// through assignment or [`mem::replace`]) to always be safe.
|
||||
/// For information on what "pinning" is, see the [`pin` module] documentation.
|
||||
///
|
||||
/// The [`Pin`][Pin] type is used instead to prevent moves through the type
|
||||
/// system. Pointers `P<T>` wrapped in the [`Pin<P<T>>`][Pin] wrapper can't be
|
||||
/// moved out of. See the [`pin` module] documentation for more information on
|
||||
/// pinning.
|
||||
/// Implementing the `Unpin` trait for `T` expresses the fact that `T` is pinning-agnostic:
|
||||
/// it shall not expose nor rely on any pinning guarantees. This, in turn, means that a
|
||||
/// `Pin`-wrapped pointer to such a type can feature a *fully unrestricted* API.
|
||||
/// In other words, if `T: Unpin`, a value of type `T` will *not* be bound by the invariants
|
||||
/// which pinning otherwise offers, even when "pinned" by a [`Pin<Ptr>`] pointing at it.
|
||||
/// When a value of type `T` is pointed at by a [`Pin<Ptr>`], [`Pin`] will not restrict access
|
||||
/// to the pointee value like it normally would, thus allowing the user to do anything that they
|
||||
/// normally could with a non-[`Pin`]-wrapped `Ptr` to that value.
|
||||
///
|
||||
/// Implementing the `Unpin` trait for `T` lifts the restrictions of pinning off
|
||||
/// the type, which then allows moving `T` out of [`Pin<P<T>>`][Pin] with
|
||||
/// functions such as [`mem::replace`].
|
||||
/// The idea of this trait is to alleviate the reduced ergonomics of APIs that require the use
|
||||
/// of [`Pin`] for soundness for some types, but which also want to be used by other types that
|
||||
/// don't care about pinning. The prime example of such an API is [`Future::poll`]. There are many
|
||||
/// [`Future`] types that don't care about pinning. These futures can implement `Unpin` and
|
||||
/// therefore get around the pinning related restrictions in the API, while still allowing the
|
||||
/// subset of [`Future`]s which *do* require pinning to be implemented soundly.
|
||||
///
|
||||
/// `Unpin` has no consequence at all for non-pinned data. In particular,
|
||||
/// [`mem::replace`] happily moves `!Unpin` data (it works for any `&mut T`, not
|
||||
/// just when `T: Unpin`). However, you cannot use [`mem::replace`] on data
|
||||
/// wrapped inside a [`Pin<P<T>>`][Pin] because you cannot get the `&mut T` you
|
||||
/// need for that, and *that* is what makes this system work.
|
||||
/// For more discussion on the consequences of [`Unpin`] within the wider scope of the pinning
|
||||
/// system, see the [section about `Unpin`] in the [`pin` module].
|
||||
///
|
||||
/// `Unpin` has no consequence at all for non-pinned data. In particular, [`mem::replace`] happily
|
||||
/// moves `!Unpin` data, which would be immovable when pinned ([`mem::replace`] works for any
|
||||
/// `&mut T`, not just when `T: Unpin`).
|
||||
///
|
||||
/// *However*, you cannot use [`mem::replace`] on `!Unpin` data which is *pinned* by being wrapped
|
||||
/// inside a [`Pin<Ptr>`] pointing at it. This is because you cannot (safely) use a
|
||||
/// [`Pin<Ptr>`] to get an `&mut T` to its pointee value, which you would need to call
|
||||
/// [`mem::replace`], and *that* is what makes this system work.
|
||||
///
|
||||
/// So this, for example, can only be done on types implementing `Unpin`:
|
||||
///
|
||||
@@ -935,11 +947,22 @@ impl<T: ?Sized> !Freeze for UnsafeCell<T> {}
|
||||
/// mem::replace(&mut *pinned_string, "other".to_string());
|
||||
/// ```
|
||||
///
|
||||
/// This trait is automatically implemented for almost every type.
|
||||
/// This trait is automatically implemented for almost every type. The compiler is free
|
||||
/// to take the conservative stance of marking types as [`Unpin`] so long as all of the types that
|
||||
/// compose its fields are also [`Unpin`]. This is because if a type implements [`Unpin`], then it
|
||||
/// is unsound for that type's implementation to rely on pinning-related guarantees for soundness,
|
||||
/// *even* when viewed through a "pinning" pointer! It is the responsibility of the implementor of
|
||||
/// a type that relies upon pinning for soundness to ensure that type is *not* marked as [`Unpin`]
|
||||
/// by adding [`PhantomPinned`] field. For more details, see the [`pin` module] docs.
|
||||
///
|
||||
/// [`mem::replace`]: crate::mem::replace
|
||||
/// [Pin]: crate::pin::Pin
|
||||
/// [`pin` module]: crate::pin
|
||||
/// [`mem::replace`]: crate::mem::replace "mem replace"
|
||||
/// [`Future`]: crate::future::Future "Future"
|
||||
/// [`Future::poll`]: crate::future::Future::poll "Future poll"
|
||||
/// [`Pin`]: crate::pin::Pin "Pin"
|
||||
/// [`Pin<Ptr>`]: crate::pin::Pin "Pin"
|
||||
/// [`pin` module]: crate::pin "pin module"
|
||||
/// [section about `Unpin`]: crate::pin#unpin "pin module docs about unpin"
|
||||
/// [`unsafe`]: ../../std/keyword.unsafe.html "keyword unsafe"
|
||||
#[stable(feature = "pin", since = "1.33.0")]
|
||||
#[diagnostic::on_unimplemented(
|
||||
note = "consider using the `pin!` macro\nconsider using `Box::pin` if you need to access the pinned value outside of the current scope",
|
||||
|
||||
+1039
-333
@@ -1,188 +1,616 @@
|
||||
//! Types that pin data to its location in memory.
|
||||
//! Types that pin data to a location in memory.
|
||||
//!
|
||||
//! It is sometimes useful to have objects that are guaranteed not to move,
|
||||
//! in the sense that their placement in memory does not change, and can thus be relied upon.
|
||||
//! A prime example of such a scenario would be building self-referential structs,
|
||||
//! as moving an object with pointers to itself will invalidate them, which could cause undefined
|
||||
//! behavior.
|
||||
//! It is sometimes useful to be able to rely upon a certain value not being able to *move*,
|
||||
//! in the sense that its address in memory cannot change. This is useful especially when there
|
||||
//! are one or more [*pointers*][pointer] pointing at that value. The ability to rely on this
|
||||
//! guarantee that the value a [pointer] is pointing at (its **pointee**) will
|
||||
//!
|
||||
//! At a high level, a <code>[Pin]\<P></code> ensures that the pointee of any pointer type
|
||||
//! `P` has a stable location in memory, meaning it cannot be moved elsewhere
|
||||
//! and its memory cannot be deallocated until it gets dropped. We say that the
|
||||
//! pointee is "pinned". Things get more subtle when discussing types that
|
||||
//! combine pinned with non-pinned data; [see below](#projections-and-structural-pinning)
|
||||
//! for more details.
|
||||
//! 1. Not be *moved* out of its memory location
|
||||
//! 2. More generally, remain *valid* at that same memory location
|
||||
//!
|
||||
//! By default, all types in Rust are movable. Rust allows passing all types by-value,
|
||||
//! and common smart-pointer types such as <code>[Box]\<T></code> and <code>[&mut] T</code> allow
|
||||
//! replacing and moving the values they contain: you can move out of a <code>[Box]\<T></code>,
|
||||
//! or you can use [`mem::swap`]. <code>[Pin]\<P></code> wraps a pointer type `P`, so
|
||||
//! <code>[Pin]<[Box]\<T>></code> functions much like a regular <code>[Box]\<T></code>:
|
||||
//! when a <code>[Pin]<[Box]\<T>></code> gets dropped, so do its contents, and the memory gets
|
||||
//! deallocated. Similarly, <code>[Pin]<[&mut] T></code> is a lot like <code>[&mut] T</code>.
|
||||
//! However, <code>[Pin]\<P></code> does not let clients actually obtain a <code>[Box]\<T></code>
|
||||
//! or <code>[&mut] T</code> to pinned data, which implies that you cannot use operations such
|
||||
//! as [`mem::swap`]:
|
||||
//! is called "pinning." We would say that a value which satisfies these guarantees has been
|
||||
//! "pinned," in that it has been permanently (until the end of its lifespan) attached to its
|
||||
//! location in memory, as though pinned to a pinboard. Pinning a value is an incredibly useful
|
||||
//! building block for [`unsafe`] code to be able to reason about whether a raw pointer to the
|
||||
//! pinned value is still valid. [As we'll see later][drop-guarantee], this is necessarily from the
|
||||
//! time the value is first pinned until the end of its lifespan. This concept of "pinning" is
|
||||
//! necessary to implement safe interfaces on top of things like self-referential types and
|
||||
//! intrusive data structures which cannot currently be modeled in fully safe Rust using only
|
||||
//! borrow-checked [references][reference].
|
||||
//!
|
||||
//! "Pinning" allows us to put a *value* which exists at some location in memory into a state where
|
||||
//! safe code cannot *move* that value to a different location in memory or otherwise invalidate it
|
||||
//! at its current location (unless it implements [`Unpin`], which we will
|
||||
//! [talk about below][self#unpin]). Anything that wants to interact with the pinned value in a way
|
||||
//! that has the potential to violate these guarantees must promise that it will not actually
|
||||
//! violate them, using the [`unsafe`] keyword to mark that such a promise is upheld by the user
|
||||
//! and not the compiler. In this way, we can allow other [`unsafe`] code to rely on any pointers
|
||||
//! that point to the pinned value to be valid to dereference while it is pinned.
|
||||
//!
|
||||
//! Note that as long as you don't use [`unsafe`], it's impossible to create or misuse a pinned
|
||||
//! value in a way that is unsound. See the documentation of [`Pin<Ptr>`] for more
|
||||
//! information on the practicalities of how to pin a value and how to use that pinned value from a
|
||||
//! user's perspective without using [`unsafe`].
|
||||
//!
|
||||
//! The rest of this documentation is intended to be the source of truth for users of [`Pin<Ptr>`]
|
||||
//! that are implementing the [`unsafe`] pieces of an interface that relies on pinning for validity;
|
||||
//! users of [`Pin<Ptr>`] in safe code do not need to read it in detail.
|
||||
//!
|
||||
//! There are several sections to this documentation:
|
||||
//!
|
||||
//! * [What is "*moving*"?][what-is-moving]
|
||||
//! * [What is "pinning"?][what-is-pinning]
|
||||
//! * [Address sensitivity, AKA "when do we need pinning?"][address-sensitive-values]
|
||||
//! * [Examples of types with address-sensitive states][address-sensitive-examples]
|
||||
//! * [Self-referential struct][self-ref]
|
||||
//! * [Intrusive, doubly-linked list][linked-list]
|
||||
//! * [Subtle details and the `Drop` guarantee][subtle-details]
|
||||
//!
|
||||
//! # What is "*moving*"?
|
||||
//! [what-is-moving]: self#what-is-moving
|
||||
//!
|
||||
//! When we say a value is *moved*, we mean that the compiler copies, byte-for-byte, the
|
||||
//! value from one location to another. In a purely mechanical sense, this is identical to
|
||||
//! [`Copy`]ing a value from one place in memory to another. In Rust, "move" carries with it the
|
||||
//! semantics of ownership transfer from one variable to another, which is the key difference
|
||||
//! between a [`Copy`] and a move. For the purposes of this module's documentation, however, when
|
||||
//! we write *move* in italics, we mean *specifically* that the value has *moved* in the mechanical
|
||||
//! sense of being located at a new place in memory.
|
||||
//!
|
||||
//! All values in Rust are trivially *moveable*. This means that the address at which a value is
|
||||
//! located is not necessarily stable in between borrows. The compiler is allowed to *move* a value
|
||||
//! to a new address without running any code to notify that value that its address
|
||||
//! has changed. Although the compiler will not insert memory *moves* where no semantic move has
|
||||
//! occurred, there are many places where a value *may* be moved. For example, when doing
|
||||
//! assignment or passing a value into a function.
|
||||
//!
|
||||
//! ```
|
||||
//! use std::pin::Pin;
|
||||
//! fn swap_pins<T>(x: Pin<&mut T>, y: Pin<&mut T>) {
|
||||
//! // `mem::swap` needs `&mut T`, but we cannot get it.
|
||||
//! // We are stuck, we cannot swap the contents of these references.
|
||||
//! // We could use `Pin::get_unchecked_mut`, but that is unsafe for a reason:
|
||||
//! // we are not allowed to use it for moving things out of the `Pin`.
|
||||
//! #[derive(Default)]
|
||||
//! struct AddrTracker(Option<usize>);
|
||||
//!
|
||||
//! impl AddrTracker {
|
||||
//! // If we haven't checked the addr of self yet, store the current
|
||||
//! // address. If we have, confirm that the current address is the same
|
||||
//! // as it was last time, or else panic.
|
||||
//! fn check_for_move(&mut self) {
|
||||
//! let current_addr = self as *mut Self as usize;
|
||||
//! match self.0 {
|
||||
//! None => self.0 = Some(current_addr),
|
||||
//! Some(prev_addr) => assert_eq!(prev_addr, current_addr),
|
||||
//! }
|
||||
//! }
|
||||
//! }
|
||||
//!
|
||||
//! // Create a tracker and store the initial address
|
||||
//! let mut tracker = AddrTracker::default();
|
||||
//! tracker.check_for_move();
|
||||
//!
|
||||
//! // Here we shadow the variable. This carries a semantic move, and may therefore also
|
||||
//! // come with a mechanical memory *move*
|
||||
//! let mut tracker = tracker;
|
||||
//!
|
||||
//! // May panic!
|
||||
//! // tracker.check_for_move();
|
||||
//! ```
|
||||
//!
|
||||
//! It is worth reiterating that <code>[Pin]\<P></code> does *not* change the fact that a Rust
|
||||
//! compiler considers all types movable. [`mem::swap`] remains callable for any `T`. Instead,
|
||||
//! <code>[Pin]\<P></code> prevents certain *values* (pointed to by pointers wrapped in
|
||||
//! <code>[Pin]\<P></code>) from being moved by making it impossible to call methods that require
|
||||
//! <code>[&mut] T</code> on them (like [`mem::swap`]).
|
||||
//! In this sense, Rust does not guarantee that `check_for_move()` will never panic, because the
|
||||
//! compiler is permitted to *move* `tracker` in many situations.
|
||||
//!
|
||||
//! <code>[Pin]\<P></code> can be used to wrap any pointer type `P`, and as such it interacts with
|
||||
//! [`Deref`] and [`DerefMut`]. A <code>[Pin]\<P></code> where <code>P: [Deref]</code> should be
|
||||
//! considered as a "`P`-style pointer" to a pinned <code>P::[Target]</code> – so, a
|
||||
//! <code>[Pin]<[Box]\<T>></code> is an owned pointer to a pinned `T`, and a
|
||||
//! <code>[Pin]<[Rc]\<T>></code> is a reference-counted pointer to a pinned `T`.
|
||||
//! For correctness, <code>[Pin]\<P></code> relies on the implementations of [`Deref`] and
|
||||
//! [`DerefMut`] not to move out of their `self` parameter, and only ever to
|
||||
//! return a pointer to pinned data when they are called on a pinned pointer.
|
||||
//! Common smart-pointer types such as [`Box<T>`] and [`&mut T`] also allow *moving* the underlying
|
||||
//! *value* they point at: you can move out of a [`Box<T>`], or you can use [`mem::replace`] to
|
||||
//! move a `T` out of a [`&mut T`]. Therefore, putting a value (such as `tracker` above) behind a
|
||||
//! pointer isn't enough on its own to ensure that its address does not change.
|
||||
//!
|
||||
//! # `Unpin`
|
||||
//! # What is "pinning"?
|
||||
//! [what-is-pinning]: self#what-is-pinning
|
||||
//!
|
||||
//! Many types are always freely movable, even when pinned, because they do not
|
||||
//! rely on having a stable address. This includes all the basic types (like
|
||||
//! [`bool`], [`i32`], and references) as well as types consisting solely of these
|
||||
//! types. Types that do not care about pinning implement the [`Unpin`]
|
||||
//! auto-trait, which cancels the effect of <code>[Pin]\<P></code>. For <code>T: [Unpin]</code>,
|
||||
//! <code>[Pin]<[Box]\<T>></code> and <code>[Box]\<T></code> function identically, as do
|
||||
//! <code>[Pin]<[&mut] T></code> and <code>[&mut] T</code>.
|
||||
//! We say that a value has been *pinned* when it has been put into a state where it is guaranteed
|
||||
//! to remain *located at the same place in memory* from the time it is pinned until its
|
||||
//! [`drop`] is called.
|
||||
//!
|
||||
//! Note that pinning and [`Unpin`] only affect the pointed-to type <code>P::[Target]</code>,
|
||||
//! not the pointer type `P` itself that got wrapped in <code>[Pin]\<P></code>. For example,
|
||||
//! whether or not <code>[Box]\<T></code> is [`Unpin`] has no effect on the behavior of
|
||||
//! <code>[Pin]<[Box]\<T>></code> (here, `T` is the pointed-to type).
|
||||
//! ## Address-sensitive values, AKA "when we need pinning"
|
||||
//! [address-sensitive-values]: self#address-sensitive-values-aka-when-we-need-pinning
|
||||
//!
|
||||
//! # Example: self-referential struct
|
||||
//! Most values in Rust are entirely okay with being *moved* around at-will.
|
||||
//! Types for which it is *always* the case that *any* value of that type can be
|
||||
//! *moved* at-will should implement [`Unpin`], which we will discuss more [below][self#unpin].
|
||||
//!
|
||||
//! Before we go into more details to explain the guarantees and choices
|
||||
//! associated with <code>[Pin]\<P></code>, we discuss some examples for how it might be used.
|
||||
//! Feel free to [skip to where the theoretical discussion continues](#drop-guarantee).
|
||||
//! [`Pin`] is specifically targeted at allowing the implementation of *safe interfaces* around
|
||||
//! types which have some state during which they become "address-sensitive." A value in such an
|
||||
//! "address-sensitive" state is *not* okay with being *moved* around at-will. Such a value must
|
||||
//! stay *un-moved* and valid during the address-sensitive portion of its lifespan because some
|
||||
//! interface is relying on those invariants to be true in order for its implementation to be sound.
|
||||
//!
|
||||
//! As a motivating example of a type which may become address-sensitive, consider a type which
|
||||
//! contains a pointer to another piece of its own data, *i.e.* a "self-referential" type. In order
|
||||
//! for such a type to be implemented soundly, the pointer which points into `self`'s data must be
|
||||
//! proven valid whenever it is accessed. But if that value is *moved*, the pointer will still
|
||||
//! point to the old address where the value was located and not into the new location of `self`,
|
||||
//! thus becoming invalid. A key example of such self-referential types are the state machines
|
||||
//! generated by the compiler to implement [`Future`] for `async fn`s.
|
||||
//!
|
||||
//! Such types that have an *address-sensitive* state usually follow a lifecycle
|
||||
//! that looks something like so:
|
||||
//!
|
||||
//! 1. A value is created which can be freely moved around.
|
||||
//! * e.g. calling an async function which returns a state machine implementing [`Future`]
|
||||
//! 2. An operation causes the value to depend on its own address not changing
|
||||
//! * e.g. calling [`poll`] for the first time on the produced [`Future`]
|
||||
//! 3. Further pieces of the safe interface of the type use internal [`unsafe`] operations which
|
||||
//! assume that the address of the value is stable
|
||||
//! * e.g. subsequent calls to [`poll`]
|
||||
//! 4. Before the value is invalidated (e.g. deallocated), it is *dropped*, giving it a chance to
|
||||
//! notify anything with pointers to itself that those pointers will be invalidated
|
||||
//! * e.g. [`drop`]ping the [`Future`] [^pin-drop-future]
|
||||
//!
|
||||
//! There are two possible ways to ensure the invariants required for 2. and 3. above (which
|
||||
//! apply to any address-sensitive type, not just self-referrential types) do not get broken.
|
||||
//!
|
||||
//! 1. Have the value detect when it is moved and update all the pointers that point to itself.
|
||||
//! 2. Guarantee that the address of the value does not change (and that memory is not re-used
|
||||
//! for anything else) during the time that the pointers to it are expected to be valid to
|
||||
//! dereference.
|
||||
//!
|
||||
//! Since, as we discussed, Rust can move values without notifying them that they have moved, the
|
||||
//! first option is ruled out.
|
||||
//!
|
||||
//! In order to implement the second option, we must in some way enforce its key invariant,
|
||||
//! *i.e.* prevent the value from being *moved* or otherwise invalidated (you may notice this
|
||||
//! sounds an awful lot like the definition of *pinning* a value). There a few ways one might be
|
||||
//! able to enforce this invariant in Rust:
|
||||
//!
|
||||
//! 1. Offer a wholly `unsafe` API to interact with the object, thus requiring every caller to
|
||||
//! uphold the invariant themselves
|
||||
//! 2. Store the value that must not be moved behind a carefully managed pointer internal to
|
||||
//! the object
|
||||
//! 3. Leverage the type system to encode and enforce this invariant by presenting a restricted
|
||||
//! API surface to interact with *any* object that requires these invariants
|
||||
//!
|
||||
//! The first option is quite obviously undesirable, as the [`unsafe`]ty of the interface will
|
||||
//! become viral throughout all code that interacts with the object.
|
||||
//!
|
||||
//! The second option is a viable solution to the problem for some use cases, in particular
|
||||
//! for self-referrential types. Under this model, any type that has an address sensitive state
|
||||
//! would ultimately store its data in something like a [`Box<T>`], carefully manage internal
|
||||
//! access to that data to ensure no *moves* or other invalidation occurs, and finally
|
||||
//! provide a safe interface on top.
|
||||
//!
|
||||
//! There are a couple of linked disadvantages to using this model. The most significant is that
|
||||
//! each individual object must assume it is *on its own* to ensure
|
||||
//! that its data does not become *moved* or otherwise invalidated. Since there is no shared
|
||||
//! contract between values of different types, an object cannot assume that others interacting
|
||||
//! with it will properly respect the invariants around interacting with its data and must
|
||||
//! therefore protect it from everyone. Because of this, *composition* of address-sensitive types
|
||||
//! requires at least a level of pointer indirection each time a new object is added to the mix
|
||||
//! (and, practically, a heap allocation).
|
||||
//!
|
||||
//! Although there were other reason as well, this issue of expensive composition is the key thing
|
||||
//! that drove Rust towards adopting a different model. It is particularly a problem
|
||||
//! when one considers, for exapmle, the implications of composing together the [`Future`]s which
|
||||
//! will eventaully make up an asynchronous task (including address-sensitive `async fn` state
|
||||
//! machines). It is plausible that there could be many layers of [`Future`]s composed together,
|
||||
//! including multiple layers of `async fn`s handling different parts of a task. It was deemed
|
||||
//! unacceptable to force indirection and allocation for each layer of composition in this case.
|
||||
//!
|
||||
//! [`Pin<Ptr>`] is an implementation of the third option. It allows us to solve the issues
|
||||
//! discussed with the second option by building a *shared contractual language* around the
|
||||
//! guarantees of "pinning" data.
|
||||
//!
|
||||
//! [^pin-drop-future]: Futures themselves do not ever need to notify other bits of code that
|
||||
//! they are being dropped, however data structures like stack-based intrusive linked lists do.
|
||||
//!
|
||||
//! ## Using [`Pin<Ptr>`] to pin values
|
||||
//!
|
||||
//! In order to pin a value, we wrap a *pointer to that value* (of some type `Ptr`) in a
|
||||
//! [`Pin<Ptr>`]. [`Pin<Ptr>`] can wrap any pointer type, forming a promise that the **pointee**
|
||||
//! will not be *moved* or [otherwise invalidated][subtle-details].
|
||||
//!
|
||||
//! We call such a [`Pin`]-wrapped pointer a **pinning pointer,** (or pinning reference, or pinning
|
||||
//! `Box`, etc.) because its existence is the thing that is conceptually pinning the underlying
|
||||
//! pointee in place: it is the metaphorical "pin" securing the data in place on the pinboard
|
||||
//! (in memory).
|
||||
//!
|
||||
//! Notice that the thing wrapped by [`Pin`] is not the value which we want to pin itself, but
|
||||
//! rather a pointer to that value! A [`Pin<Ptr>`] does not pin the `Ptr`; instead, it pins the
|
||||
//! pointer's ***pointee** value*.
|
||||
//!
|
||||
//! ### Pinning as a library contract
|
||||
//!
|
||||
//! Pinning does not require nor make use of any compiler "magic"[^noalias], only a specific
|
||||
//! contract between the [`unsafe`] parts of a library API and its users.
|
||||
//!
|
||||
//! It is important to stress this point as a user of the [`unsafe`] parts of the [`Pin`] API.
|
||||
//! Practically, this means that performing the mechanics of "pinning" a value by creating a
|
||||
//! [`Pin<Ptr>`] to it *does not* actually change the way the compiler behaves towards the
|
||||
//! inner value! It is possible to use incorrect [`unsafe`] code to create a [`Pin<Ptr>`] to a
|
||||
//! value which does not actually satisfy the invariants that a pinned value must satisfy, and in
|
||||
//! this way lead to undefined behavior even in (from that point) fully safe code. Similarly, using
|
||||
//! [`unsafe`], one may get access to a bare [`&mut T`] from a [`Pin<Ptr>`] and
|
||||
//! use that to invalidly *move* the pinned value out. It is the job of the user of the
|
||||
//! [`unsafe`] parts of the [`Pin`] API to ensure these invariants are not violated.
|
||||
//!
|
||||
//! This differs from e.g. [`UnsafeCell`] which changes the semantics of a program's compiled
|
||||
//! output. A [`Pin<Ptr>`] is a handle to a value which we have promised we will not move out of,
|
||||
//! but Rust still considers all values themselves to be fundamentally moveable through, *e.g.*
|
||||
//! assignment or [`mem::replace`].
|
||||
//!
|
||||
//! [^noalias]: There is a bit of nuance here that is still being decided about what the aliasing
|
||||
//! semantics of `Pin<&mut T>` should be, but this is true as of today.
|
||||
//!
|
||||
//! ### How [`Pin`] prevents misuse in safe code
|
||||
//!
|
||||
//! In order to accomplish the goal of pinning the pointee value, [`Pin<Ptr>`] restricts access to
|
||||
//! the wrapped `Ptr` type in safe code. Specifically, [`Pin`] disallows the ability to access
|
||||
//! the wrapped pointer in ways that would allow the user to *move* the underlying pointee value or
|
||||
//! otherwise re-use that memory for something else without using [`unsafe`]. For example, a
|
||||
//! [`Pin<&mut T>`] makes it impossible to obtain the wrapped <code>[&mut] T</code> safely because
|
||||
//! through that <code>[&mut] T</code> it would be possible to *move* the underlying value out of
|
||||
//! the pointer with [`mem::replace`], etc.
|
||||
//!
|
||||
//! As discussed above, this promise must be upheld manually by [`unsafe`] code which interacts
|
||||
//! with the [`Pin<Ptr>`] so that other [`unsafe`] code can rely on the pointee value being
|
||||
//! *un-moved* and valid. Interfaces that operate on values which are in an address-sensitive state
|
||||
//! accept an argument like <code>[Pin]<[&mut] T></code> or <code>[Pin]<[Box]\<T>></code> to
|
||||
//! indicate this contract to the caller.
|
||||
//!
|
||||
//! [As discussed below][drop-guarantee], opting in to using pinning guarantees in the interface
|
||||
//! of an address-sensitive type has consequences for the implementation of some safe traits on
|
||||
//! that type as well.
|
||||
//!
|
||||
//! ## Interaction between [`Deref`] and [`Pin<Ptr>`]
|
||||
//!
|
||||
//! Since [`Pin<Ptr>`] can wrap any pointer type, it uses [`Deref`] and [`DerefMut`] in
|
||||
//! order to identify the type of the pinned pointee data and provide (restricted) access to it.
|
||||
//!
|
||||
//! A [`Pin<Ptr>`] where [`Ptr: Deref`][Deref] is a "`Ptr`-style pinning pointer" to a pinned
|
||||
//! [`Ptr::Target`][Target] – so, a <code>[Pin]<[Box]\<T>></code> is an owned, pinning pointer to a
|
||||
//! pinned `T`, and a <code>[Pin]<[Rc]\<T>></code> is a reference-counted, pinning pointer to a
|
||||
//! pinned `T`.
|
||||
//!
|
||||
//! [`Pin<Ptr>`] also uses the [`<Ptr as Deref>::Target`][Target] type information to modify the
|
||||
//! interface it is allowed to provide for interacting with that data (for example, when a
|
||||
//! pinning pointer points at pinned data which implements [`Unpin`], as
|
||||
//! [discussed below][self#unpin]).
|
||||
//!
|
||||
//! [`Pin<Ptr>`] requires that implementations of [`Deref`] and [`DerefMut`] on `Ptr` return a
|
||||
//! pointer to the pinned data directly and do not *move* out of the `self` parameter during their
|
||||
//! implementation of [`DerefMut::deref_mut`]. It is unsound for [`unsafe`] code to wrap pointer
|
||||
//! types with such "malicious" implementations of [`Deref`]; see [`Pin<Ptr>::new_unchecked`] for
|
||||
//! details.
|
||||
//!
|
||||
//! ## Fixing `AddrTracker`
|
||||
//!
|
||||
//! The guarantee of a stable address is necessary to make our `AddrTracker` example work. When
|
||||
//! `check_for_move` sees a <code>[Pin]<&mut AddrTracker></code>, it can safely assume that value
|
||||
//! will exist at that same address until said value goes out of scope, and thus multiple calls
|
||||
//! to it *cannot* panic.
|
||||
//!
|
||||
//! ```
|
||||
//! use std::marker::PhantomPinned;
|
||||
//! use std::pin::Pin;
|
||||
//! use std::pin::pin;
|
||||
//!
|
||||
//! #[derive(Default)]
|
||||
//! struct AddrTracker {
|
||||
//! prev_addr: Option<usize>,
|
||||
//! // remove auto-implemented `Unpin` bound to mark this type as having some
|
||||
//! // address-sensitive state. This is essential for our expected pinning
|
||||
//! // guarantees to work, and is discussed more below.
|
||||
//! _pin: PhantomPinned,
|
||||
//! }
|
||||
//!
|
||||
//! impl AddrTracker {
|
||||
//! fn check_for_move(self: Pin<&mut Self>) {
|
||||
//! let current_addr = &*self as *const Self as usize;
|
||||
//! match self.prev_addr {
|
||||
//! None => {
|
||||
//! // SAFETY: we do not move out of self
|
||||
//! let self_data_mut = unsafe { self.get_unchecked_mut() };
|
||||
//! self_data_mut.prev_addr = Some(current_addr);
|
||||
//! },
|
||||
//! Some(prev_addr) => assert_eq!(prev_addr, current_addr),
|
||||
//! }
|
||||
//! }
|
||||
//! }
|
||||
//!
|
||||
//! // 1. Create the value, not yet in an address-sensitive state
|
||||
//! let tracker = AddrTracker::default();
|
||||
//!
|
||||
//! // 2. Pin the value by putting it behind a pinning pointer, thus putting
|
||||
//! // it into an address-sensitive state
|
||||
//! let mut ptr_to_pinned_tracker: Pin<&mut AddrTracker> = pin!(tracker);
|
||||
//! ptr_to_pinned_tracker.as_mut().check_for_move();
|
||||
//!
|
||||
//! // Trying to access `tracker` or pass `ptr_to_pinned_tracker` to anything that requires
|
||||
//! // mutable access to a non-pinned version of it will no longer compile
|
||||
//!
|
||||
//! // 3. We can now assume that the tracker value will never be moved, thus
|
||||
//! // this will never panic!
|
||||
//! ptr_to_pinned_tracker.as_mut().check_for_move();
|
||||
//! ```
|
||||
//!
|
||||
//! Note that this invariant is enforced by simply making it impossible to call code that would
|
||||
//! perform a move on the pinned value. This is the case since the only way to access that pinned
|
||||
//! value is through the pinning <code>[Pin]<[&mut] T>></code>, which in turn restricts our access.
|
||||
//!
|
||||
//! ## [`Unpin`]
|
||||
//!
|
||||
//! The vast majority of Rust types have no address-sensitive states. These types
|
||||
//! implement the [`Unpin`] auto-trait, which cancels the restrictive effects of
|
||||
//! [`Pin`] when the *pointee* type `T` is [`Unpin`]. When [`T: Unpin`][Unpin],
|
||||
//! <code>[Pin]<[Box]\<T>></code> functions identically to a non-pinning [`Box<T>`]; similarly,
|
||||
//! <code>[Pin]<[&mut] T></code> would impose no additional restrictions above a regular
|
||||
//! [`&mut T`].
|
||||
//!
|
||||
//! The idea of this trait is to alleviate the reduced ergonomics of APIs that require the use
|
||||
//! of [`Pin`] for soundness for some types, but which also want to be used by other types that
|
||||
//! don't care about pinning. The prime example of such an API is [`Future::poll`]. There are many
|
||||
//! [`Future`] types that don't care about pinning. These futures can implement [`Unpin`] and
|
||||
//! therefore get around the pinning related restrictions in the API, while still allowing the
|
||||
//! subset of [`Future`]s which *do* require pinning to be implemented soundly.
|
||||
//!
|
||||
//! Note that the interaction between a [`Pin<Ptr>`] and [`Unpin`] is through the type of the
|
||||
//! **pointee** value, [`<Ptr as Deref>::Target`][Target]. Whether the `Ptr` type itself
|
||||
//! implements [`Unpin`] does not affect the behavior of a [`Pin<Ptr>`]. For example, whether or not
|
||||
//! [`Box`] is [`Unpin`] has no effect on the behavior of <code>[Pin]<[Box]\<T>></code>, because
|
||||
//! `T` is the type of the pointee value, not [`Box`]. So, whether `T` implements [`Unpin`] is
|
||||
//! the thing that will affect the behavior of the <code>[Pin]<[Box]\<T>></code>.
|
||||
//!
|
||||
//! Builtin types that are [`Unpin`] include all of the primitive types, like [`bool`], [`i32`],
|
||||
//! and [`f32`], references (<code>[&]T</code> and <code>[&mut] T</code>), etc., as well as many
|
||||
//! core and standard library types like [`Box<T>`], [`String`], and more.
|
||||
//! These types are marked [`Unpin`] because they do not have an ddress-sensitive state like the
|
||||
//! ones we discussed above. If they did have such a state, those parts of their interface would be
|
||||
//! unsound without being expressed through pinning, and they would then need to not
|
||||
//! implement [`Unpin`].
|
||||
//!
|
||||
//! The compiler is free to take the conservative stance of marking types as [`Unpin`] so long as
|
||||
//! all of the types that compose its fields are also [`Unpin`]. This is because if a type
|
||||
//! implements [`Unpin`], then it is unsound for that type's implementation to rely on
|
||||
//! pinning-related guarantees for soundness, *even* when viewed through a "pinning" pointer! It is
|
||||
//! the responsibility of the implementor of a type that relies upon pinning for soundness to
|
||||
//! ensure that type is *not* marked as [`Unpin`] by adding [`PhantomPinned`] field. This is
|
||||
//! exactly what we did with our `AddrTracker` example above. Without doing this, you *must not*
|
||||
//! rely on pinning-related guarantees to apply to your type!
|
||||
//!
|
||||
//! If need to truly pin a value of a foreign or built-in type that implements [`Unpin`], you'll
|
||||
//! need to create your own wrapper type around the [`Unpin`] type you want to pin and then
|
||||
//! opts-out of [`Unpin`] using [`PhantomPinned`].
|
||||
//!
|
||||
//! Exposing access to the inner field which you want to remain pinned must then be carefully
|
||||
//! considered as well! Remember, exposing a method that gives access to a
|
||||
//! <code>[Pin]<[&mut] InnerT>></code> where `InnerT: [Unpin]` would allow safe code to trivially
|
||||
//! move the inner value out of that pinning pointer, which is precisely what you're seeking to
|
||||
//! prevent! Exposing a field of a pinned value through a pinning pointer is called "projecting"
|
||||
//! a pin, and the more general case of deciding in which cases a pin should be able to be
|
||||
//! projected or not is called "structural pinning." We will go into more detail about this
|
||||
//! [below][structural-pinning].
|
||||
//!
|
||||
//! # Examples of address-sensitive types
|
||||
//! [address-sensitive-examples]: #examples-of-address-sensitive-types
|
||||
//!
|
||||
//! ## A self-referential struct
|
||||
//! [self-ref]: #a-self-referential-struct
|
||||
//! [`Unmovable`]: #a-self-referential-struct
|
||||
//!
|
||||
//! Self-referential structs are the simplest kind of address-sensitive type.
|
||||
//!
|
||||
//! It is often useful for a struct to hold a pointer back into itself, which
|
||||
//! allows the program to efficiently track subsections of the struct.
|
||||
//! Below, the `slice` field is a pointer into the `data` field, which
|
||||
//! we could imagine being used to track a sliding window of `data` in parser
|
||||
//! code.
|
||||
//!
|
||||
//! As mentioned before, this pattern is also used extensively by compiler-generated
|
||||
//! [`Future`]s.
|
||||
//!
|
||||
//! ```rust
|
||||
//! use std::pin::Pin;
|
||||
//! use std::marker::PhantomPinned;
|
||||
//! use std::ptr::NonNull;
|
||||
//!
|
||||
//! // This is a self-referential struct because the slice field points to the data field.
|
||||
//! // We cannot inform the compiler about that with a normal reference,
|
||||
//! // as this pattern cannot be described with the usual borrowing rules.
|
||||
//! // Instead we use a raw pointer, though one which is known not to be null,
|
||||
//! // as we know it's pointing at the string.
|
||||
//! /// This is a self-referential struct because `self.slice` points into `self.data`.
|
||||
//! struct Unmovable {
|
||||
//! data: String,
|
||||
//! slice: NonNull<String>,
|
||||
//! /// Backing buffer.
|
||||
//! data: [u8; 64],
|
||||
//! /// Points at `self.data` which we know is itself non-null. Raw pointer because we can't do
|
||||
//! /// this with a normal reference.
|
||||
//! slice: NonNull<[u8]>,
|
||||
//! /// Suppress `Unpin` so that this cannot be moved out of a `Pin` once constructed.
|
||||
//! _pin: PhantomPinned,
|
||||
//! }
|
||||
//!
|
||||
//! impl Unmovable {
|
||||
//! // To ensure the data doesn't move when the function returns,
|
||||
//! // we place it in the heap where it will stay for the lifetime of the object,
|
||||
//! // and the only way to access it would be through a pointer to it.
|
||||
//! fn new(data: String) -> Pin<Box<Self>> {
|
||||
//! /// Create a new `Unmovable`.
|
||||
//! ///
|
||||
//! /// To ensure the data doesn't move we place it on the heap behind a pinning Box.
|
||||
//! /// Note that the data is pinned, but the `Pin<Box<Self>>` which is pinning it can
|
||||
//! /// itself still be moved. This is important because it means we can return the pinning
|
||||
//! /// pointer from the function, which is itself a kind of move!
|
||||
//! fn new() -> Pin<Box<Self>> {
|
||||
//! let res = Unmovable {
|
||||
//! data,
|
||||
//! // we only create the pointer once the data is in place
|
||||
//! // otherwise it will have already moved before we even started
|
||||
//! slice: NonNull::dangling(),
|
||||
//! data: [0; 64],
|
||||
//! // We only create the pointer once the data is in place
|
||||
//! // otherwise it will have already moved before we even started.
|
||||
//! slice: NonNull::from(&[]),
|
||||
//! _pin: PhantomPinned,
|
||||
//! };
|
||||
//! let mut boxed = Box::pin(res);
|
||||
//! // First we put the data in a box, which will be its final resting place
|
||||
//! let mut boxed = Box::new(res);
|
||||
//!
|
||||
//! let slice = NonNull::from(&boxed.data);
|
||||
//! // we know this is safe because modifying a field doesn't move the whole struct
|
||||
//! unsafe {
|
||||
//! let mut_ref: Pin<&mut Self> = Pin::as_mut(&mut boxed);
|
||||
//! Pin::get_unchecked_mut(mut_ref).slice = slice;
|
||||
//! }
|
||||
//! boxed
|
||||
//! // Then we make the slice field point to the proper part of that boxed data.
|
||||
//! // From now on we need to make sure we don't move the boxed data.
|
||||
//! boxed.slice = NonNull::from(&boxed.data);
|
||||
//!
|
||||
//! // To do that, we pin the data in place by pointing to it with a pinning
|
||||
//! // (`Pin`-wrapped) pointer.
|
||||
//! //
|
||||
//! // `Box::into_pin` makes existing `Box` pin the data in-place without moving it,
|
||||
//! // so we can safely do this now *after* inserting the slice pointer above, but we have
|
||||
//! // to take care that we haven't performed any other semantic moves of `res` in between.
|
||||
//! let pin = Box::into_pin(boxed);
|
||||
//!
|
||||
//! // Now we can return the pinned (through a pinning Box) data
|
||||
//! pin
|
||||
//! }
|
||||
//! }
|
||||
//!
|
||||
//! let unmoved = Unmovable::new("hello".to_string());
|
||||
//! // The pointer should point to the correct location,
|
||||
//! // so long as the struct hasn't moved.
|
||||
//! let unmovable: Pin<Box<Unmovable>> = Unmovable::new();
|
||||
//!
|
||||
//! // The inner pointee `Unmovable` struct will now never be allowed to move.
|
||||
//! // Meanwhile, we are free to move the pointer around.
|
||||
//! # #[allow(unused_mut)]
|
||||
//! let mut still_unmoved = unmoved;
|
||||
//! let mut still_unmoved = unmovable;
|
||||
//! assert_eq!(still_unmoved.slice, NonNull::from(&still_unmoved.data));
|
||||
//!
|
||||
//! // Since our type doesn't implement Unpin, this will fail to compile:
|
||||
//! // let mut new_unmoved = Unmovable::new("world".to_string());
|
||||
//! // We cannot mutably dereference a `Pin<Ptr>` unless the pointee is `Unpin` or we use unsafe.
|
||||
//! // Since our type doesn't implement `Unpin`, this will fail to compile.
|
||||
//! // let mut new_unmoved = Unmovable::new();
|
||||
//! // std::mem::swap(&mut *still_unmoved, &mut *new_unmoved);
|
||||
//! ```
|
||||
//!
|
||||
//! # Example: intrusive doubly-linked list
|
||||
//! ## An intrusive, doubly-linked list
|
||||
//! [linked-list]: #an-intrusive-doubly-linked-list
|
||||
//!
|
||||
//! In an intrusive doubly-linked list, the collection does not actually allocate
|
||||
//! the memory for the elements itself. Allocation is controlled by the clients,
|
||||
//! and elements can live on a stack frame that lives shorter than the collection does.
|
||||
//! In an intrusive doubly-linked list, the collection itself does not own the memory in which
|
||||
//! each of its elements is stored. Instead, each client is free to allocate space for elements it
|
||||
//! adds to the list in whichever manner it likes, including on the stack! Elements can live on a
|
||||
//! stack frame that lives shorter than the collection does provided the elements that live in a
|
||||
//! given stack frame are removed from the list before going out of scope.
|
||||
//!
|
||||
//! To make this work, every element has pointers to its predecessor and successor in
|
||||
//! the list. Elements can only be added when they are pinned, because moving the elements
|
||||
//! around would invalidate the pointers. Moreover, the [`Drop`][Drop] implementation of a linked
|
||||
//! list element will patch the pointers of its predecessor and successor to remove itself
|
||||
//! from the list.
|
||||
//! To make such an intrusive data structure work, every element stores pointers to its predecessor
|
||||
//! and successor within its own data, rather than having the list structure itself managing those
|
||||
//! pointers. It is in this sense that the structure is "intrusive": the details of how an
|
||||
//! element is stored within the larger structure "intrudes" on the implementation of the element
|
||||
//! type itself!
|
||||
//!
|
||||
//! Crucially, we have to be able to rely on [`drop`] being called. If an element
|
||||
//! could be deallocated or otherwise invalidated without calling [`drop`], the pointers into it
|
||||
//! from its neighboring elements would become invalid, which would break the data structure.
|
||||
//! The full implementation details of such a data structure are outside the scope of this
|
||||
//! documentation, but we will discuss how [`Pin`] can help to do so.
|
||||
//!
|
||||
//! Therefore, pinning also comes with a [`drop`]-related guarantee.
|
||||
//! Using such an intrusive pattern, elements may only be added when they are pinned. If we think
|
||||
//! about the consequences of adding non-pinned values to such a list, this becomes clear:
|
||||
//!
|
||||
//! # `Drop` guarantee
|
||||
//! *Moving* or otherwise invalidating an element's data would invalidate the pointers back to it
|
||||
//! which are stored in the elements ahead and behind it. Thus, in order to soundly dereference
|
||||
//! the pointers stored to the next and previous elements, we must satisfy the guarantee that
|
||||
//! nothing has invalidated those pointers (which point to data that we do not own).
|
||||
//!
|
||||
//! The purpose of pinning is to be able to rely on the placement of some data in memory.
|
||||
//! To make this work, not just moving the data is restricted; deallocating, repurposing, or
|
||||
//! otherwise invalidating the memory used to store the data is restricted, too.
|
||||
//! Concretely, for pinned data you have to maintain the invariant
|
||||
//! that *its memory will not get invalidated or repurposed from the moment it gets pinned until
|
||||
//! when [`drop`] is called*. Only once [`drop`] returns or panics, the memory may be reused.
|
||||
//! Moreover, the [`Drop`][Drop] implementation of each element must in some way notify its
|
||||
//! predecessor and successor elements that it should be removed from the list before it is fully
|
||||
//! destroyed, otherwise the pointers back to it would again become invalidated.
|
||||
//!
|
||||
//! Memory can be "invalidated" by deallocation, but also by
|
||||
//! replacing a <code>[Some]\(v)</code> by [`None`], or calling [`Vec::set_len`] to "kill" some
|
||||
//! elements off of a vector. It can be repurposed by using [`ptr::write`] to overwrite it without
|
||||
//! calling the destructor first. None of this is allowed for pinned data without calling [`drop`].
|
||||
//! Crucially, this means we have to be able to rely on [`drop`] always being called before an
|
||||
//! element is invalidated. If an element could be deallocated or otherwise invalidated without
|
||||
//! calling [`drop`], the pointers to it stored in its neighboring elements would
|
||||
//! become invalid, which would break the data structure.
|
||||
//!
|
||||
//! This is exactly the kind of guarantee that the intrusive linked list from the previous
|
||||
//! section needs to function correctly.
|
||||
//! Therefore, pinning data also comes with [the "`Drop` guarantee"][drop-guarantee].
|
||||
//!
|
||||
//! Notice that this guarantee does *not* mean that memory does not leak! It is still
|
||||
//! completely okay to not ever call [`drop`] on a pinned element (e.g., you can still
|
||||
//! call [`mem::forget`] on a <code>[Pin]<[Box]\<T>></code>). In the example of the doubly-linked
|
||||
//! list, that element would just stay in the list. However you must not free or reuse the storage
|
||||
//! *without calling [`drop`]*.
|
||||
//! # Subtle details and the `Drop` guarantee
|
||||
//! [subtle-details]: self#subtle-details-and-the-drop-guarantee
|
||||
//! [drop-guarantee]: self#subtle-details-and-the-drop-guarantee
|
||||
//!
|
||||
//! # `Drop` implementation
|
||||
//! The purpose of pinning is not *just* to prevent a value from being *moved*, but more
|
||||
//! generally to be able to rely on the pinned value *remaining valid **at a specific place*** in
|
||||
//! memory.
|
||||
//!
|
||||
//! If your type uses pinning (such as the two examples above), you have to be careful
|
||||
//! when implementing [`Drop`][Drop]. The [`drop`] function takes <code>[&mut] self</code>, but this
|
||||
//! is called *even if your type was previously pinned*! It is as if the
|
||||
//! compiler automatically called [`Pin::get_unchecked_mut`].
|
||||
//! To do so, pinning a value adds an *additional* invariant that must be upheld in order for use
|
||||
//! of the pinned data to be valid, on top of the ones that must be upheld for a non-pinned value
|
||||
//! of the same type to be valid:
|
||||
//!
|
||||
//! This can never cause a problem in safe code because implementing a type that
|
||||
//! relies on pinning requires unsafe code, but be aware that deciding to make
|
||||
//! use of pinning in your type (for example by implementing some operation on
|
||||
//! <code>[Pin]<[&]Self></code> or <code>[Pin]<[&mut] Self></code>) has consequences for your
|
||||
//! From the moment a value is pinned by constructing a [`Pin`]ning pointer to it, that value
|
||||
//! must *remain, **valid***, at that same address in memory, *until its [`drop`] handler is
|
||||
//! called.*
|
||||
//!
|
||||
//! There is some subtlety to this which we have not yet talked about in detail. The invariant
|
||||
//! described above means that, yes,
|
||||
//!
|
||||
//! 1. The value must not be moved out of its location in memory
|
||||
//!
|
||||
//! but it also implies that,
|
||||
//!
|
||||
//! 2. The memory location that stores the value must not get invalidated or otherwise repurposed
|
||||
//! during the lifespan of the pinned value until its [`drop`] returns or panics
|
||||
//!
|
||||
//! This point is subtle but required for intrusive data structures to be implemented soundly.
|
||||
//!
|
||||
//! ## `Drop` guarantee
|
||||
//!
|
||||
//! There needs to be a way for a pinned value to notify any code that is relying on its pinned
|
||||
//! status that it is about to be destroyed. In this way, the dependent code can remove the
|
||||
//! pinned value's address from its data structures or otherwise change its behavior with the
|
||||
//! knowledge that it can no longer rely on that value existing at the location it was pinned to.
|
||||
//!
|
||||
//! Thus, in any situation where we may want to overwrite a pinned value, that value's [`drop`] must
|
||||
//! be called beforehand (unless the pinned value implements [`Unpin`], in which case we can ignore
|
||||
//! all of [`Pin`]'s guarantees, as usual).
|
||||
//!
|
||||
//! The most common storage-reuse situations occur when a value on the stack is destroyed as part
|
||||
//! of a function return and when heap storage is freed. In both cases, [`drop`] gets run for us
|
||||
//! by Rust when using standard safe code. However, for manual heap allocations or otherwise
|
||||
//! custom-allocated storage, [`unsafe`] code must make sure to call [`ptr::drop_in_place`] before
|
||||
//! deallocating and re-using said storage.
|
||||
//!
|
||||
//! In addition, storage "re-use"/invalidation can happen even if no storage is (de-)allocated.
|
||||
//! For example, if we had an [`Option`] which contained a `Some(v)` where `v` is pinned, then `v`
|
||||
//! would be invalidated by setting that option to `None`.
|
||||
//!
|
||||
//! Similarly, if a [`Vec`] was used to store pinned values and [`Vec::set_len`] was used to
|
||||
//! manually "kill" some elements of a vector, all of the items "killed" would become invalidated,
|
||||
//! which would be *undefined behavior* if those items were pinned.
|
||||
//!
|
||||
//! Both of these cases are somewhat contrived, but it is crucial to remember that [`Pin`]ned data
|
||||
//! *must* be [`drop`]ped before it is invalidated; not just to prevent memory leaks, but as a
|
||||
//! matter of soundness. As a corollary, the following code can *never* be made safe:
|
||||
//!
|
||||
//! ```rust
|
||||
//! # use std::mem::ManuallyDrop;
|
||||
//! # use std::pin::Pin;
|
||||
//! # struct Type;
|
||||
//! // Pin something inside a `ManuallyDrop`. This is fine on its own.
|
||||
//! let mut pin: Pin<Box<ManuallyDrop<Type>>> = Box::pin(ManuallyDrop::new(Type));
|
||||
//!
|
||||
//! // However, creating a pinning mutable reference to the type *inside*
|
||||
//! // the `ManuallyDrop` is not!
|
||||
//! let inner: Pin<&mut Type> = unsafe {
|
||||
//! Pin::map_unchecked_mut(pin.as_mut(), |x| &mut **x)
|
||||
//! };
|
||||
//! ```
|
||||
//!
|
||||
//! Because [`mem::ManuallyDrop`] inhibits the destructor of `Type`, it won't get run when the
|
||||
//! <code>[Box]<[ManuallyDrop]\<Type>></code> is dropped, thus violating the drop guarantee of the
|
||||
//! <code>[Pin]<[&mut] Type>></code>.
|
||||
//!
|
||||
//! Of course, *leaking* memory in such a way that its underlying storage will never get invalidated
|
||||
//! or re-used is still fine: [`mem::forget`]ing a [`Box<T>`] prevents its storage from ever getting
|
||||
//! re-used, so the [`drop`] guarantee is still satisfied.
|
||||
//!
|
||||
//! # Implementing an address-sensitive type.
|
||||
//!
|
||||
//! This section goes into detail on important considerations for implementing your own
|
||||
//! address-sensitive types, which are different from merely using [`Pin<Ptr>`] in a generic
|
||||
//! way.
|
||||
//!
|
||||
//! ## Implementing [`Drop`] for types with address-sensitive states
|
||||
//! [drop-impl]: self#implementing-drop-for-types-with-address-sensitive-states
|
||||
//!
|
||||
//! The [`drop`] function takes [`&mut self`], but this is called *even if that `self` has been
|
||||
//! pinned*! Implementing [`Drop`] for a type with address-sensitive states, because if `self` was
|
||||
//! indeed in an address-sensitive state before [`drop`] was called, it is as if the compiler
|
||||
//! automatically called [`Pin::get_unchecked_mut`].
|
||||
//!
|
||||
//! This can never cause a problem in purely safe code because creating a pinning pointer to
|
||||
//! a type which has an address-sensitive (thus does not implement `Unpin`) requires `unsafe`,
|
||||
//! but it is important to note that choosing to take advantage of pinning-related guarantees
|
||||
//! to justify validity in the implementation of your type has consequences for that type's
|
||||
//! [`Drop`][Drop] implementation as well: if an element of your type could have been pinned,
|
||||
//! you must treat [`Drop`][Drop] as implicitly taking <code>[Pin]<[&mut] Self></code>.
|
||||
//! you must treat [`Drop`][Drop] as implicitly taking <code>self: [Pin]<[&mut] Self></code>.
|
||||
//!
|
||||
//! For example, you could implement [`Drop`][Drop] as follows:
|
||||
//! You should implement [`Drop`] as follows:
|
||||
//!
|
||||
//! ```rust,no_run
|
||||
//! # use std::pin::Pin;
|
||||
//! # struct Type { }
|
||||
//! # struct Type;
|
||||
//! impl Drop for Type {
|
||||
//! fn drop(&mut self) {
|
||||
//! // `new_unchecked` is okay because we know this value is never used
|
||||
@@ -195,72 +623,157 @@
|
||||
//! }
|
||||
//! ```
|
||||
//!
|
||||
//! The function `inner_drop` has the type that [`drop`] *should* have, so this makes sure that
|
||||
//! you do not accidentally use `self`/`this` in a way that is in conflict with pinning.
|
||||
//! The function `inner_drop` has the signature that [`drop`] *should* have in this situation.
|
||||
//! This makes sure that you do not accidentally use `self`/`this` in a way that is in conflict
|
||||
//! with pinning's invariants.
|
||||
//!
|
||||
//! Moreover, if your type is `#[repr(packed)]`, the compiler will automatically
|
||||
//! Moreover, if your type is [`#[repr(packed)]`][packed], the compiler will automatically
|
||||
//! move fields around to be able to drop them. It might even do
|
||||
//! that for fields that happen to be sufficiently aligned. As a consequence, you cannot use
|
||||
//! pinning with a `#[repr(packed)]` type.
|
||||
//! pinning with a [`#[repr(packed)]`][packed] type.
|
||||
//!
|
||||
//! # Projections and Structural Pinning
|
||||
//! ### Implementing [`Drop`] for pointer types which will be used as [`Pin`]ning pointers
|
||||
//!
|
||||
//! When working with pinned structs, the question arises how one can access the
|
||||
//! fields of that struct in a method that takes just <code>[Pin]<[&mut] Struct></code>.
|
||||
//! The usual approach is to write helper methods (so called *projections*)
|
||||
//! that turn <code>[Pin]<[&mut] Struct></code> into a reference to the field, but what type should
|
||||
//! that reference have? Is it <code>[Pin]<[&mut] Field></code> or <code>[&mut] Field</code>?
|
||||
//! The same question arises with the fields of an `enum`, and also when considering
|
||||
//! container/wrapper types such as <code>[Vec]\<T></code>, <code>[Box]\<T></code>,
|
||||
//! or <code>[RefCell]\<T></code>. (This question applies to both mutable and shared references,
|
||||
//! we just use the more common case of mutable references here for illustration.)
|
||||
//! It should further be noted that creating a pinning pointer of some type `Ptr` *also* carries
|
||||
//! with it implications on the way that `Ptr` type must implement [`Drop`]
|
||||
//! (as well as [`Deref`] and [`DerefMut`])! When implementing a pointer type that may be used as
|
||||
//! a pinning pointer, you must also take the same care described above not to *move* out of or
|
||||
//! otherwise invalidate the pointee during [`Drop`], [`Deref`], or [`DerefMut`]
|
||||
//! implementations.
|
||||
//!
|
||||
//! It turns out that it is actually up to the author of the data structure to decide whether
|
||||
//! the pinned projection for a particular field turns <code>[Pin]<[&mut] Struct></code>
|
||||
//! into <code>[Pin]<[&mut] Field></code> or <code>[&mut] Field</code>. There are some
|
||||
//! constraints though, and the most important constraint is *consistency*:
|
||||
//! every field can be *either* projected to a pinned reference, *or* have
|
||||
//! pinning removed as part of the projection. If both are done for the same field,
|
||||
//! that will likely be unsound!
|
||||
//! ## "Assigning" pinned data
|
||||
//!
|
||||
//! As the author of a data structure you get to decide for each field whether pinning
|
||||
//! Although in general it is not valid to swap data or assign through a [`Pin<Ptr>`] for the same
|
||||
//! reason that reusing a pinned object's memory is invalid, it is possible to do validly when
|
||||
//! implemented with special care for the needs of the exact data structure which is being
|
||||
//! modified. For example, the assigning function must know how to update all uses of the pinned
|
||||
//! address (and any other invariants necessary to satisfy validity for that type). For
|
||||
//! [`Unmovable`] (from the example above), we could write an assignment function like so:
|
||||
//!
|
||||
//! ```
|
||||
//! # use std::pin::Pin;
|
||||
//! # use std::marker::PhantomPinned;
|
||||
//! # use std::ptr::NonNull;
|
||||
//! # struct Unmovable {
|
||||
//! # data: [u8; 64],
|
||||
//! # slice: NonNull<[u8]>,
|
||||
//! # _pin: PhantomPinned,
|
||||
//! # }
|
||||
//! #
|
||||
//! impl Unmovable {
|
||||
//! // Copies the contents of `src` into `self`, fixing up the self-pointer
|
||||
//! // in the process.
|
||||
//! fn assign(self: Pin<&mut Self>, src: Pin<&mut Self>) {
|
||||
//! unsafe {
|
||||
//! let unpinned_self = Pin::into_inner_unchecked(self);
|
||||
//! let unpinned_src = Pin::into_inner_unchecked(src);
|
||||
//! *unpinned_self = Self {
|
||||
//! data: unpinned_src.data,
|
||||
//! slice: NonNull::from(&mut []),
|
||||
//! _pin: PhantomPinned,
|
||||
//! };
|
||||
//!
|
||||
//! let data_ptr = unpinned_src.data.as_ptr() as *const u8;
|
||||
//! let slice_ptr = unpinned_src.slice.as_ptr() as *const u8;
|
||||
//! let offset = slice_ptr.offset_from(data_ptr) as usize;
|
||||
//! let len = (*unpinned_src.slice.as_ptr()).len();
|
||||
//!
|
||||
//! unpinned_self.slice = NonNull::from(&mut unpinned_self.data[offset..offset+len]);
|
||||
//! }
|
||||
//! }
|
||||
//! }
|
||||
//! ```
|
||||
//!
|
||||
//! Even though we can't have the compiler do the assignment for us, it's possible to write
|
||||
//! such specialized functions for types that might need it.
|
||||
//!
|
||||
//! Note that it _is_ possible to assign generically through a [`Pin<Ptr>`] by way of [`Pin::set()`].
|
||||
//! This does not violate any guarantees, since it will run [`drop`] on the pointee value before
|
||||
//! assigning the new value. Thus, the [`drop`] implementation still has a chance to perform the
|
||||
//! necessary notifications to dependent values before the memory location of the original pinned
|
||||
//! value is overwritten.
|
||||
//!
|
||||
//! ## Projections and Structural Pinning
|
||||
//! [structural-pinning]: self#projections-and-structural-pinning
|
||||
//!
|
||||
//! With ordinary structs, it is natural that we want to add *projection* methods that allow
|
||||
//! borrowing one or more of the inner fields of a struct when the caller has access to a
|
||||
//! borrow of the whole struct:
|
||||
//!
|
||||
//! ```
|
||||
//! # struct Field;
|
||||
//! struct Struct {
|
||||
//! field: Field,
|
||||
//! // ...
|
||||
//! }
|
||||
//!
|
||||
//! impl Struct {
|
||||
//! fn field(&mut self) -> &mut Field { &mut self.field }
|
||||
//! }
|
||||
//! ```
|
||||
//!
|
||||
//! When working with address-sensitive types, it's not obvious what the signature of these
|
||||
//! functions should be. If `field` takes <code>self: [Pin]<[&mut Struct][&mut]></code>, should it
|
||||
//! return [`&mut Field`] or <code>[Pin]<[`&mut Field`]></code>? This question also arises with
|
||||
//! `enum`s and wrapper types like [`Vec<T>`], [`Box<T>`], and [`RefCell<T>`]. (This question
|
||||
//! applies just as well to shared references, but we'll examine the more common case of mutable
|
||||
//! references for illustration)
|
||||
//!
|
||||
//! It turns out that it's up to the author of `Struct` to decide which type the "projection"
|
||||
//! should produce. The choice must be *consistent* though: if a pin is projected to a field
|
||||
//! in one place, then it should very likely not be exposed elsewhere without projecting the
|
||||
//! pin.
|
||||
//!
|
||||
//! As the author of a data structure, you get to decide for each field whether pinning
|
||||
//! "propagates" to this field or not. Pinning that propagates is also called "structural",
|
||||
//! because it follows the structure of the type.
|
||||
//! In the following subsections, we describe the considerations that have to be made
|
||||
//! for either choice.
|
||||
//!
|
||||
//! ## Pinning *is not* structural for `field`
|
||||
//! This choice depends on what guarantees you need from the field for your [`unsafe`] code to work.
|
||||
//! If the field is itself address-sensitive, or participates in the parent struct's address
|
||||
//! sensitivity, it will need to be structurally pinned.
|
||||
//!
|
||||
//! It may seem counter-intuitive that the field of a pinned struct might not be pinned,
|
||||
//! but that is actually the easiest choice: if a <code>[Pin]<[&mut] Field></code> is never created,
|
||||
//! nothing can go wrong! So, if you decide that some field does not have structural pinning,
|
||||
//! all you have to ensure is that you never create a pinned reference to that field.
|
||||
//! A useful test is if [`unsafe`] code that consumes <code>[Pin]\<[&mut Struct][&mut]></code>
|
||||
//! also needs to take note of the address of the field itself, it may be evidence that that field
|
||||
//! is structurally pinned. Unfortunately, there are no hard-and-fast rules.
|
||||
//!
|
||||
//! ### Choosing pinning *not to be* structural for `field`...
|
||||
//!
|
||||
//! While counter-intuitive, it's often the easier choice: if you do not expose a
|
||||
//! <code>[Pin]<[&mut] Field></code>, you do not need to be careful about other code
|
||||
//! moving out of that field, you just have to ensure is that you never create pinning
|
||||
//! reference to that field. This does of course also mean that if you decide a field does not
|
||||
//! have structural pinning, you must not write [`unsafe`] code that assumes (invalidly) that the
|
||||
//! field *is* structurally pinned!
|
||||
//!
|
||||
//! Fields without structural pinning may have a projection method that turns
|
||||
//! <code>[Pin]<[&mut] Struct></code> into <code>[&mut] Field</code>:
|
||||
//! <code>[Pin]<[&mut] Struct></code> into [`&mut Field`]:
|
||||
//!
|
||||
//! ```rust,no_run
|
||||
//! # use std::pin::Pin;
|
||||
//! # type Field = i32;
|
||||
//! # struct Struct { field: Field }
|
||||
//! impl Struct {
|
||||
//! fn pin_get_field(self: Pin<&mut Self>) -> &mut Field {
|
||||
//! // This is okay because `field` is never considered pinned.
|
||||
//! fn field(self: Pin<&mut Self>) -> &mut Field {
|
||||
//! // This is okay because `field` is never considered pinned, therefore we do not
|
||||
//! // need to uphold any pinning guarantees for this field in particular. Of course,
|
||||
//! // we must not elsewhere assume this field *is* pinned if we choose to expose
|
||||
//! // such a method!
|
||||
//! unsafe { &mut self.get_unchecked_mut().field }
|
||||
//! }
|
||||
//! }
|
||||
//! ```
|
||||
//!
|
||||
//! You may also <code>impl [Unpin] for Struct</code> *even if* the type of `field`
|
||||
//! is not [`Unpin`]. What that type thinks about pinning is not relevant
|
||||
//! when no <code>[Pin]<[&mut] Field></code> is ever created.
|
||||
//! You may also in this situation <code>impl [Unpin] for Struct {}</code> *even if* the type of
|
||||
//! `field` is not [`Unpin`]. Since we have explicitly chosen not to care about pinning guarantees
|
||||
//! for `field`, the way `field`'s type interacts with pinning is no longer relevant in the
|
||||
//! context of its use in `Struct`.
|
||||
//!
|
||||
//! ## Pinning *is* structural for `field`
|
||||
//! ### Choosing pinning *to be* structural for `field`...
|
||||
//!
|
||||
//! The other option is to decide that pinning is "structural" for `field`,
|
||||
//! meaning that if the struct is pinned then so is the field.
|
||||
//!
|
||||
//! This allows writing a projection that creates a <code>[Pin]<[&mut] Field></code>, thus
|
||||
//! This allows writing a projection that creates a <code>[Pin]<[`&mut Field`]></code>, thus
|
||||
//! witnessing that the field is pinned:
|
||||
//!
|
||||
//! ```rust,no_run
|
||||
@@ -268,108 +781,117 @@
|
||||
//! # type Field = i32;
|
||||
//! # struct Struct { field: Field }
|
||||
//! impl Struct {
|
||||
//! fn pin_get_field(self: Pin<&mut Self>) -> Pin<&mut Field> {
|
||||
//! fn field(self: Pin<&mut Self>) -> Pin<&mut Field> {
|
||||
//! // This is okay because `field` is pinned when `self` is.
|
||||
//! unsafe { self.map_unchecked_mut(|s| &mut s.field) }
|
||||
//! }
|
||||
//! }
|
||||
//! ```
|
||||
//!
|
||||
//! However, structural pinning comes with a few extra requirements:
|
||||
//! Structural pinning comes with a few extra requirements:
|
||||
//!
|
||||
//! 1. The struct must only be [`Unpin`] if all the structural fields are
|
||||
//! [`Unpin`]. This is the default, but [`Unpin`] is a safe trait, so as the author of
|
||||
//! the struct it is your responsibility *not* to add something like
|
||||
//! <code>impl\<T> [Unpin] for Struct\<T></code>. (Notice that adding a projection operation
|
||||
//! requires unsafe code, so the fact that [`Unpin`] is a safe trait does not break
|
||||
//! the principle that you only have to worry about any of this if you use [`unsafe`].)
|
||||
//! 2. The destructor of the struct must not move structural fields out of its argument. This
|
||||
//! is the exact point that was raised in the [previous section][drop-impl]: [`drop`] takes
|
||||
//! <code>[&mut] self</code>, but the struct (and hence its fields) might have been pinned
|
||||
//! before. You have to guarantee that you do not move a field inside your [`Drop`][Drop]
|
||||
//! implementation. In particular, as explained previously, this means that your struct
|
||||
//! must *not* be `#[repr(packed)]`.
|
||||
//! See that section for how to write [`drop`] in a way that the compiler can help you
|
||||
//! not accidentally break pinning.
|
||||
//! 3. You must make sure that you uphold the [`Drop` guarantee][drop-guarantee]:
|
||||
//! once your struct is pinned, the memory that contains the
|
||||
//! content is not overwritten or deallocated without calling the content's destructors.
|
||||
//! This can be tricky, as witnessed by <code>[VecDeque]\<T></code>: the destructor of
|
||||
//! <code>[VecDeque]\<T></code> can fail to call [`drop`] on all elements if one of the
|
||||
//! destructors panics. This violates the [`Drop`][Drop] guarantee, because it can lead to
|
||||
//! elements being deallocated without their destructor being called.
|
||||
//! (<code>[VecDeque]\<T></code> has no pinning projections, so this
|
||||
//! does not cause unsoundness.)
|
||||
//! 4. You must not offer any other operations that could lead to data being moved out of
|
||||
//! 1. *Structural [`Unpin`].* A struct can be [`Unpin`] only if all of its
|
||||
//! structurally-pinned fields are, too. This is [`Unpin`]'s behavior by default.
|
||||
//! However, as a libray author, it is your responsibility not to write something like
|
||||
//! <code>impl\<T> [Unpin] for Struct\<T> {}</code> and then offer a method that provides
|
||||
//! structural pinning to an inner field of `T`, which may not be [`Unpin`]! (Adding *any*
|
||||
//! projection operation requires unsafe code, so the fact that [`Unpin`] is a safe trait does
|
||||
//! not break the principle that you only have to worry about any of this if you use
|
||||
//! [`unsafe`])
|
||||
//!
|
||||
//! 2. *Pinned Destruction.* As discussed [above][drop-impl], [`drop`] takes
|
||||
//! [`&mut self`], but the struct (and hence its fields) might have been pinned
|
||||
//! before. The destructor must be written as if its argument was
|
||||
//! <code>self: [Pin]\<[`&mut Self`]></code>, instead.
|
||||
//!
|
||||
//! As a consequence, the struct *must not* be [`#[repr(packed)]`][packed].
|
||||
//!
|
||||
//! 3. *Structural Notice of Destruction.* You must uphold the the
|
||||
//! [`Drop` guarantee][drop-guarantee]: once your struct is pinned, the struct's storage cannot
|
||||
//! be re-used without calling the structurally-pinned fields' destructors, as well.
|
||||
//!
|
||||
//! This can be tricky, as witnessed by [`VecDeque<T>`]: the destructor of [`VecDeque<T>`]
|
||||
//! can fail to call [`drop`] on all elements if one of the destructors panics. This violates
|
||||
//! the [`Drop` guarantee][drop-guarantee], because it can lead to elements being deallocated
|
||||
//! without their destructor being called.
|
||||
//!
|
||||
//! [`VecDeque<T>`] has no pinning projections, so its destructor is sound. If it wanted
|
||||
//! to provide such structural pinning, its destructor would need to abort the process if any
|
||||
//! of the destructors panicked.
|
||||
//!
|
||||
//! 4. You must not offer any other operations that could lead to data being *moved* out of
|
||||
//! the structural fields when your type is pinned. For example, if the struct contains an
|
||||
//! <code>[Option]\<T></code> and there is a [`take`][Option::take]-like operation with type
|
||||
//! <code>fn([Pin]<[&mut] Struct\<T>>) -> [Option]\<T></code>,
|
||||
//! that operation can be used to move a `T` out of a pinned `Struct<T>` – which means
|
||||
//! pinning cannot be structural for the field holding this data.
|
||||
//! [`Option<T>`] and there is a [`take`][Option::take]-like operation with type
|
||||
//! <code>fn([Pin]<[&mut Struct\<T>][&mut]>) -> [`Option<T>`]</code>,
|
||||
//! then that operation can be used to move a `T` out of a pinned `Struct<T>` – which
|
||||
//! means pinning cannot be structural for the field holding this data.
|
||||
//!
|
||||
//! For a more complex example of moving data out of a pinned type,
|
||||
//! imagine if <code>[RefCell]\<T></code> had a method
|
||||
//! <code>fn get_pin_mut(self: [Pin]<[&mut] Self>) -> [Pin]<[&mut] T></code>.
|
||||
//! imagine if [`RefCell<T>`] had a method
|
||||
//! <code>fn get_pin_mut(self: [Pin]<[`&mut Self`]>) -> [Pin]<[`&mut T`]></code>.
|
||||
//! Then we could do the following:
|
||||
//! ```compile_fail
|
||||
//! # use std::cell::RefCell;
|
||||
//! # use std::pin::Pin;
|
||||
//! fn exploit_ref_cell<T>(rc: Pin<&mut RefCell<T>>) {
|
||||
//! { let p = rc.as_mut().get_pin_mut(); } // Here we get pinned access to the `T`.
|
||||
//! let rc_shr: &RefCell<T> = rc.into_ref().get_ref();
|
||||
//! let b = rc_shr.borrow_mut();
|
||||
//! let content = &mut *b; // And here we have `&mut T` to the same data.
|
||||
//! // Here we get pinned access to the `T`.
|
||||
//! let _: Pin<&mut T> = rc.as_mut().get_pin_mut();
|
||||
//!
|
||||
//! // And here we have `&mut T` to the same data.
|
||||
//! let shared: &RefCell<T> = rc.into_ref().get_ref();
|
||||
//! let borrow = shared.borrow_mut();
|
||||
//! let content = &mut *borrow;
|
||||
//! }
|
||||
//! ```
|
||||
//! This is catastrophic, it means we can first pin the content of the
|
||||
//! <code>[RefCell]\<T></code> (using <code>[RefCell]::get_pin_mut</code>) and then move that
|
||||
//! This is catastrophic: it means we can first pin the content of the
|
||||
//! [`RefCell<T>`] (using <code>[RefCell]::get_pin_mut</code>) and then move that
|
||||
//! content using the mutable reference we got later.
|
||||
//!
|
||||
//! ## Examples
|
||||
//! ### Structural Pinning examples
|
||||
//!
|
||||
//! For a type like <code>[Vec]\<T></code>, both possibilities (structural pinning or not) make
|
||||
//! sense. A <code>[Vec]\<T></code> with structural pinning could have `get_pin`/`get_pin_mut`
|
||||
//! methods to get pinned references to elements. However, it could *not* allow calling
|
||||
//! [`pop`][Vec::pop] on a pinned <code>[Vec]\<T></code> because that would move the (structurally
|
||||
//! For a type like [`Vec<T>`], both possibilities (structural pinning or not) make
|
||||
//! sense. A [`Vec<T>`] with structural pinning could have `get_pin`/`get_pin_mut`
|
||||
//! methods to get pinning references to elements. However, it could *not* allow calling
|
||||
//! [`pop`][Vec::pop] on a pinned [`Vec<T>`] because that would move the (structurally
|
||||
//! pinned) contents! Nor could it allow [`push`][Vec::push], which might reallocate and thus also
|
||||
//! move the contents.
|
||||
//!
|
||||
//! A <code>[Vec]\<T></code> without structural pinning could
|
||||
//! <code>impl\<T> [Unpin] for [Vec]\<T></code>, because the contents are never pinned
|
||||
//! and the <code>[Vec]\<T></code> itself is fine with being moved as well.
|
||||
//! A [`Vec<T>`] without structural pinning could
|
||||
//! <code>impl\<T> [Unpin] for [`Vec<T>`]</code>, because the contents are never pinned
|
||||
//! and the [`Vec<T>`] itself is fine with being moved as well.
|
||||
//! At that point pinning just has no effect on the vector at all.
|
||||
//!
|
||||
//! In the standard library, pointer types generally do not have structural pinning,
|
||||
//! and thus they do not offer pinning projections. This is why <code>[Box]\<T>: [Unpin]</code>
|
||||
//! and thus they do not offer pinning projections. This is why <code>[`Box<T>`]: [Unpin]</code>
|
||||
//! holds for all `T`. It makes sense to do this for pointer types, because moving the
|
||||
//! <code>[Box]\<T></code> does not actually move the `T`: the <code>[Box]\<T></code> can be freely
|
||||
//! movable (aka [`Unpin`]) even if the `T` is not. In fact, even <code>[Pin]<[Box]\<T>></code> and
|
||||
//! <code>[Pin]<[&mut] T></code> are always [`Unpin`] themselves, for the same reason:
|
||||
//! [`Box<T>`] does not actually move the `T`: the [`Box<T>`] can be freely
|
||||
//! movable (aka [`Unpin`]) even if the `T` is not. In fact, even <code>[Pin]<[`Box<T>`]></code> and
|
||||
//! <code>[Pin]<[`&mut T`]></code> are always [`Unpin`] themselves, for the same reason:
|
||||
//! their contents (the `T`) are pinned, but the pointers themselves can be moved without moving
|
||||
//! the pinned data. For both <code>[Box]\<T></code> and <code>[Pin]<[Box]\<T>></code>,
|
||||
//! the pinned data. For both [`Box<T>`] and <code>[Pin]<[`Box<T>`]></code>,
|
||||
//! whether the content is pinned is entirely independent of whether the
|
||||
//! pointer is pinned, meaning pinning is *not* structural.
|
||||
//!
|
||||
//! When implementing a [`Future`] combinator, you will usually need structural pinning
|
||||
//! for the nested futures, as you need to get pinned references to them to call [`poll`].
|
||||
//! But if your combinator contains any other data that does not need to be pinned,
|
||||
//! for the nested futures, as you need to get pinning ([`Pin`]-wrapped) references to them to
|
||||
//! call [`poll`]. But if your combinator contains any other data that does not need to be pinned,
|
||||
//! you can make those fields not structural and hence freely access them with a
|
||||
//! mutable reference even when you just have <code>[Pin]<[&mut] Self></code> (such as in your own
|
||||
//! [`poll`] implementation).
|
||||
//! mutable reference even when you just have <code>[Pin]<[`&mut Self`]></code>
|
||||
//! (such as in your own [`poll`] implementation).
|
||||
//!
|
||||
//! [`&mut T`]: &mut
|
||||
//! [`&mut self`]: &mut
|
||||
//! [`&mut Self`]: &mut
|
||||
//! [`&mut Field`]: &mut
|
||||
//! [Deref]: crate::ops::Deref "ops::Deref"
|
||||
//! [`Deref`]: crate::ops::Deref "ops::Deref"
|
||||
//! [Target]: crate::ops::Deref::Target "ops::Deref::Target"
|
||||
//! [`DerefMut`]: crate::ops::DerefMut "ops::DerefMut"
|
||||
//! [`mem::swap`]: crate::mem::swap "mem::swap"
|
||||
//! [`mem::forget`]: crate::mem::forget "mem::forget"
|
||||
//! [Vec]: ../../std/vec/struct.Vec.html "Vec"
|
||||
//! [`Vec::set_len`]: ../../std/vec/struct.Vec.html#method.set_len "Vec::set_len"
|
||||
//! [Box]: ../../std/boxed/struct.Box.html "Box"
|
||||
//! [Vec::pop]: ../../std/vec/struct.Vec.html#method.pop "Vec::pop"
|
||||
//! [Vec::push]: ../../std/vec/struct.Vec.html#method.push "Vec::push"
|
||||
//! [Rc]: ../../std/rc/struct.Rc.html "rc::Rc"
|
||||
//! [ManuallyDrop]: crate::mem::ManuallyDrop "ManuallyDrop"
|
||||
//! [RefCell]: crate::cell::RefCell "cell::RefCell"
|
||||
//! [`drop`]: Drop::drop
|
||||
//! [VecDeque]: ../../std/collections/struct.VecDeque.html "collections::VecDeque"
|
||||
//! [`ptr::write`]: crate::ptr::write "ptr::write"
|
||||
//! [`Future`]: crate::future::Future "future::Future"
|
||||
//! [drop-impl]: #drop-implementation
|
||||
@@ -378,6 +900,23 @@
|
||||
//! [&]: reference "shared reference"
|
||||
//! [&mut]: reference "mutable reference"
|
||||
//! [`unsafe`]: ../../std/keyword.unsafe.html "keyword unsafe"
|
||||
//! [packed]: https://doc.rust-lang.org/nomicon/other-reprs.html#reprpacked
|
||||
//! [`std::alloc`]: ../../std/alloc/index.html
|
||||
//! [`Box<T>`]: ../../std/boxed/struct.Box.html
|
||||
//! [Box]: ../../std/boxed/struct.Box.html "Box"
|
||||
//! [`Box`]: ../../std/boxed/struct.Box.html "Box"
|
||||
//! [`Rc<T>`]: ../../std/rc/struct.Rc.html
|
||||
//! [Rc]: ../../std/rc/struct.Rc.html "rc::Rc"
|
||||
//! [`Vec<T>`]: ../../std/vec/struct.Vec.html
|
||||
//! [Vec]: ../../std/vec/struct.Vec.html "Vec"
|
||||
//! [`Vec`]: ../../std/vec/struct.Vec.html "Vec"
|
||||
//! [`Vec::set_len`]: ../../std/vec/struct.Vec.html#method.set_len "Vec::set_len"
|
||||
//! [Vec::pop]: ../../std/vec/struct.Vec.html#method.pop "Vec::pop"
|
||||
//! [Vec::push]: ../../std/vec/struct.Vec.html#method.push "Vec::push"
|
||||
//! [`Vec::set_len`]: ../../std/vec/struct.Vec.html#method.set_len
|
||||
//! [`VecDeque<T>`]: ../../std/collections/struct.VecDeque.html
|
||||
//! [VecDeque]: ../../std/collections/struct.VecDeque.html "collections::VecDeque"
|
||||
//! [`String`]: ../../std/string/struct.String.html "String"
|
||||
|
||||
#![stable(feature = "pin", since = "1.33.0")]
|
||||
|
||||
@@ -386,17 +925,159 @@
|
||||
use crate::hash::{Hash, Hasher};
|
||||
use crate::ops::{CoerceUnsized, Deref, DerefMut, DispatchFromDyn, Receiver};
|
||||
|
||||
/// A pinned pointer.
|
||||
#[allow(unused_imports)]
|
||||
use crate::{
|
||||
cell::{RefCell, UnsafeCell},
|
||||
future::Future,
|
||||
marker::PhantomPinned,
|
||||
mem, ptr,
|
||||
};
|
||||
|
||||
/// A pointer which pins its pointee in place.
|
||||
///
|
||||
/// This is a wrapper around a kind of pointer which makes that pointer "pin" its
|
||||
/// value in place, preventing the value referenced by that pointer from being moved
|
||||
/// unless it implements [`Unpin`].
|
||||
/// [`Pin`] is a wrapper around some kind of pointer `Ptr` which makes that pointer "pin" its
|
||||
/// pointee value in place, thus preventing the value referenced by that pointer from being moved
|
||||
/// or otherwise invalidated at that place in memory unless it implements [`Unpin`].
|
||||
///
|
||||
/// `Pin<P>` is guaranteed to have the same memory layout and ABI as `P`.
|
||||
/// *See the [`pin` module] documentation for a more thorough exploration of pinning.*
|
||||
///
|
||||
/// *See the [`pin` module] documentation for an explanation of pinning.*
|
||||
/// ## Pinning values with [`Pin<Ptr>`]
|
||||
///
|
||||
/// [`pin` module]: self
|
||||
/// In order to pin a value, we wrap a *pointer to that value* (of some type `Ptr`) in a
|
||||
/// [`Pin<Ptr>`]. [`Pin<Ptr>`] can wrap any pointer type, forming a promise that the **pointee**
|
||||
/// will not be *moved* or [otherwise invalidated][subtle-details]. If the pointee value's type
|
||||
/// implements [`Unpin`], we are free to disregard these requirements entirely and can wrap any
|
||||
/// pointer to that value in [`Pin`] directly via [`Pin::new`]. If the pointee value's type does
|
||||
/// not implement [`Unpin`], then Rust will not let us use the [`Pin::new`] function directly and
|
||||
/// we'll need to construct a [`Pin`]-wrapped pointer in one of the more specialized manners
|
||||
/// discussed below.
|
||||
///
|
||||
/// We call such a [`Pin`]-wrapped pointer a **pinning pointer** (or pinning ref, or pinning
|
||||
/// [`Box`], etc.) because its existince is the thing that is pinning the underlying pointee in
|
||||
/// place: it is the metaphorical "pin" securing the data in place on the pinboard (in memory).
|
||||
///
|
||||
/// It is important to stress that the thing in the [`Pin`] is not the value which we want to pin
|
||||
/// itself, but rather a pointer to that value! A [`Pin<Ptr>`] does not pin the `Ptr` but rather
|
||||
/// the pointer's ***pointee** value*.
|
||||
///
|
||||
/// The most common set of types which require pinning related guarantees for soundness are the
|
||||
/// compiler-generated state machines that implement [`Future`] for the return value of
|
||||
/// `async fn`s. These compiler-generated [`Future`]s may contain self-referrential pointers, one
|
||||
/// of the most common use cases for [`Pin`]. More details on this point are provided in the
|
||||
/// [`pin` module] docs, but suffice it to say they require the guarantees provided by pinning to
|
||||
/// be implemented soundly.
|
||||
///
|
||||
/// This requirement for the implementation of `async fn`s means that the [`Future`] trait
|
||||
/// requires all calls to [`poll`] to use a <code>self: [Pin]\<&mut Self></code> parameter instead
|
||||
/// of the usual `&mut self`. Therefore, when manually polling a future, you will need to pin it
|
||||
/// first.
|
||||
///
|
||||
/// You may notice that `async fn`-sourced [`Future`]s are only a small percentage of all
|
||||
/// [`Future`]s that exist, yet we had to modify the signature of [`poll`] for all [`Future`]s
|
||||
/// to accommodate them. This is unfortunate, but there is a way that the language attempts to
|
||||
/// alleviate the extra friction that this API choice incurs: the [`Unpin`] trait.
|
||||
///
|
||||
/// The vast majority of Rust types have no reason to ever care about being pinned. These
|
||||
/// types implement the [`Unpin`] trait, which entirely opts all values of that type out of
|
||||
/// pinning-related guarantees. For values of these types, pinning a value by pointing to it with a
|
||||
/// [`Pin<Ptr>`] will have no actual effect.
|
||||
///
|
||||
/// The reason this distinction exists is exactly to allow APIs like [`Future::poll`] to take a
|
||||
/// [`Pin<Ptr>`] as an argument for all types while only forcing [`Future`] types that actually
|
||||
/// care about pinning guarantees pay the ergonomics cost. For the majority of [`Future`] types
|
||||
/// that don't have a reason to care about being pinned and therefore implement [`Unpin`], the
|
||||
/// <code>[Pin]\<&mut Self></code> will act exactly like a regular `&mut Self`, allowing direct
|
||||
/// access to the underlying value. Only types that *don't* implement [`Unpin`] will be restricted.
|
||||
///
|
||||
/// ### Pinning a value of a type that implements [`Unpin`]
|
||||
///
|
||||
/// If the type of the value you need to "pin" implements [`Unpin`], you can trivially wrap any
|
||||
/// pointer to that value in a [`Pin`] by calling [`Pin::new`].
|
||||
///
|
||||
/// ```
|
||||
/// use std::pin::Pin;
|
||||
///
|
||||
/// // Create a value of a type that implements `Unpin`
|
||||
/// let mut unpin_future = std::future::ready(5);
|
||||
///
|
||||
/// // Pin it by creating a pinning mutable reference to it (ready to be `poll`ed!)
|
||||
/// let my_pinned_unpin_future: Pin<&mut _> = Pin::new(&mut unpin_future);
|
||||
/// ```
|
||||
///
|
||||
/// ### Pinning a value inside a [`Box`]
|
||||
///
|
||||
/// The simplest and most flexible way to pin a value that does not implement [`Unpin`] is to put
|
||||
/// that value inside a [`Box`] and then turn that [`Box`] into a "pinning [`Box`]" by wrapping it
|
||||
/// in a [`Pin`]. You can do both of these in a single step using [`Box::pin`]. Let's see an
|
||||
/// example of using this flow to pin a [`Future`] returned from calling an `async fn`, a common
|
||||
/// use case as described above.
|
||||
///
|
||||
/// ```
|
||||
/// use std::pin::Pin;
|
||||
///
|
||||
/// async fn add_one(x: u32) -> u32 {
|
||||
/// x + 1
|
||||
/// }
|
||||
///
|
||||
/// // Call the async function to get a future back
|
||||
/// let fut = add_one(42);
|
||||
///
|
||||
/// // Pin the future inside a pinning box
|
||||
/// let pinned_fut: Pin<Box<_>> = Box::pin(fut);
|
||||
/// ```
|
||||
///
|
||||
/// If you have a value which is already boxed, for example a [`Box<dyn Future>`][Box], you can pin
|
||||
/// that value in-place at its current memory address using [`Box::into_pin`].
|
||||
///
|
||||
/// ```
|
||||
/// use std::pin::Pin;
|
||||
/// use std::future::Future;
|
||||
///
|
||||
/// async fn add_one(x: u32) -> u32 {
|
||||
/// x + 1
|
||||
/// }
|
||||
///
|
||||
/// fn boxed_add_one(x: u32) -> Box<dyn Future<Output = u32>> {
|
||||
/// Box::new(add_one(x))
|
||||
/// }
|
||||
///
|
||||
/// let boxed_fut = boxed_add_one(42);
|
||||
///
|
||||
/// // Pin the future inside the existing box
|
||||
/// let pinned_fut: Pin<Box<_>> = Box::into_pin(boxed_fut);
|
||||
/// ```
|
||||
///
|
||||
/// There are similar pinning methods offered on the other standard library smart pointer types
|
||||
/// as well, like [`Rc`] and [`Arc`].
|
||||
///
|
||||
/// ### Pinning a value on the stack using [`pin!`]
|
||||
///
|
||||
/// There are some situations where it is desirable or even required (for example, in a `#[no_std]`
|
||||
/// context where you don't have access to the standard library or allocation in general) to
|
||||
/// pin a value which does not implement [`Unpin`] to its location on the stack. Doing so is
|
||||
/// possible using the [`pin!`] macro. See its documentation for more.
|
||||
///
|
||||
/// ## Layout and ABI
|
||||
///
|
||||
/// [`Pin<Ptr>`] is guaranteed to have the same memory layout and ABI[^noalias] as `Ptr`.
|
||||
///
|
||||
/// [^noalias]: There is a bit of nuance here that is still being decided about whether the
|
||||
/// aliasing semantics of `Pin<&mut T>` should be different than `&mut T`, but this is true as of
|
||||
/// today.
|
||||
///
|
||||
/// [`pin!`]: crate::pin::pin "pin!"
|
||||
/// [`Future`]: crate::future::Future "Future"
|
||||
/// [`poll`]: crate::future::Future::poll "Future::poll"
|
||||
/// [`Future::poll`]: crate::future::Future::poll "Future::poll"
|
||||
/// [`pin` module]: self "pin module"
|
||||
/// [`Rc`]: ../../std/rc/struct.Rc.html "Rc"
|
||||
/// [`Arc`]: ../../std/sync/struct.Arc.html "Arc"
|
||||
/// [Box]: ../../std/boxed/struct.Box.html "Box"
|
||||
/// [`Box`]: ../../std/boxed/struct.Box.html "Box"
|
||||
/// [`Box::pin`]: ../../std/boxed/struct.Box.html#method.pin "Box::pin"
|
||||
/// [`Box::into_pin`]: ../../std/boxed/struct.Box.html#method.into_pin "Box::into_pin"
|
||||
/// [subtle-details]: self#subtle-details-and-the-drop-guarantee "pin subtle details"
|
||||
/// [`unsafe`]: ../../std/keyword.unsafe.html "keyword unsafe"
|
||||
//
|
||||
// Note: the `Clone` derive below causes unsoundness as it's possible to implement
|
||||
// `Clone` for mutable references.
|
||||
@@ -406,7 +1087,7 @@
|
||||
#[fundamental]
|
||||
#[repr(transparent)]
|
||||
#[derive(Copy, Clone)]
|
||||
pub struct Pin<P> {
|
||||
pub struct Pin<Ptr> {
|
||||
// FIXME(#93176): this field is made `#[unstable] #[doc(hidden)] pub` to:
|
||||
// - deter downstream users from accessing it (which would be unsound!),
|
||||
// - let the `pin!` macro access it (such a macro requires using struct
|
||||
@@ -414,7 +1095,7 @@ pub struct Pin<P> {
|
||||
// Long-term, `unsafe` fields or macro hygiene are expected to offer more robust alternatives.
|
||||
#[unstable(feature = "unsafe_pin_internals", issue = "none")]
|
||||
#[doc(hidden)]
|
||||
pub pointer: P,
|
||||
pub pointer: Ptr,
|
||||
}
|
||||
|
||||
// The following implementations aren't derived in order to avoid soundness
|
||||
@@ -424,68 +1105,68 @@ pub struct Pin<P> {
|
||||
// See <https://internals.rust-lang.org/t/unsoundness-in-pin/11311/73> for more details.
|
||||
|
||||
#[stable(feature = "pin_trait_impls", since = "1.41.0")]
|
||||
impl<P: Deref, Q: Deref> PartialEq<Pin<Q>> for Pin<P>
|
||||
impl<Ptr: Deref, Q: Deref> PartialEq<Pin<Q>> for Pin<Ptr>
|
||||
where
|
||||
P::Target: PartialEq<Q::Target>,
|
||||
Ptr::Target: PartialEq<Q::Target>,
|
||||
{
|
||||
fn eq(&self, other: &Pin<Q>) -> bool {
|
||||
P::Target::eq(self, other)
|
||||
Ptr::Target::eq(self, other)
|
||||
}
|
||||
|
||||
fn ne(&self, other: &Pin<Q>) -> bool {
|
||||
P::Target::ne(self, other)
|
||||
Ptr::Target::ne(self, other)
|
||||
}
|
||||
}
|
||||
|
||||
#[stable(feature = "pin_trait_impls", since = "1.41.0")]
|
||||
impl<P: Deref<Target: Eq>> Eq for Pin<P> {}
|
||||
impl<Ptr: Deref<Target: Eq>> Eq for Pin<Ptr> {}
|
||||
|
||||
#[stable(feature = "pin_trait_impls", since = "1.41.0")]
|
||||
impl<P: Deref, Q: Deref> PartialOrd<Pin<Q>> for Pin<P>
|
||||
impl<Ptr: Deref, Q: Deref> PartialOrd<Pin<Q>> for Pin<Ptr>
|
||||
where
|
||||
P::Target: PartialOrd<Q::Target>,
|
||||
Ptr::Target: PartialOrd<Q::Target>,
|
||||
{
|
||||
fn partial_cmp(&self, other: &Pin<Q>) -> Option<cmp::Ordering> {
|
||||
P::Target::partial_cmp(self, other)
|
||||
Ptr::Target::partial_cmp(self, other)
|
||||
}
|
||||
|
||||
fn lt(&self, other: &Pin<Q>) -> bool {
|
||||
P::Target::lt(self, other)
|
||||
Ptr::Target::lt(self, other)
|
||||
}
|
||||
|
||||
fn le(&self, other: &Pin<Q>) -> bool {
|
||||
P::Target::le(self, other)
|
||||
Ptr::Target::le(self, other)
|
||||
}
|
||||
|
||||
fn gt(&self, other: &Pin<Q>) -> bool {
|
||||
P::Target::gt(self, other)
|
||||
Ptr::Target::gt(self, other)
|
||||
}
|
||||
|
||||
fn ge(&self, other: &Pin<Q>) -> bool {
|
||||
P::Target::ge(self, other)
|
||||
Ptr::Target::ge(self, other)
|
||||
}
|
||||
}
|
||||
|
||||
#[stable(feature = "pin_trait_impls", since = "1.41.0")]
|
||||
impl<P: Deref<Target: Ord>> Ord for Pin<P> {
|
||||
impl<Ptr: Deref<Target: Ord>> Ord for Pin<Ptr> {
|
||||
fn cmp(&self, other: &Self) -> cmp::Ordering {
|
||||
P::Target::cmp(self, other)
|
||||
Ptr::Target::cmp(self, other)
|
||||
}
|
||||
}
|
||||
|
||||
#[stable(feature = "pin_trait_impls", since = "1.41.0")]
|
||||
impl<P: Deref<Target: Hash>> Hash for Pin<P> {
|
||||
impl<Ptr: Deref<Target: Hash>> Hash for Pin<Ptr> {
|
||||
fn hash<H: Hasher>(&self, state: &mut H) {
|
||||
P::Target::hash(self, state);
|
||||
Ptr::Target::hash(self, state);
|
||||
}
|
||||
}
|
||||
|
||||
impl<P: Deref<Target: Unpin>> Pin<P> {
|
||||
/// Construct a new `Pin<P>` around a pointer to some data of a type that
|
||||
impl<Ptr: Deref<Target: Unpin>> Pin<Ptr> {
|
||||
/// Construct a new `Pin<Ptr>` around a pointer to some data of a type that
|
||||
/// implements [`Unpin`].
|
||||
///
|
||||
/// Unlike `Pin::new_unchecked`, this method is safe because the pointer
|
||||
/// `P` dereferences to an [`Unpin`] type, which cancels the pinning guarantees.
|
||||
/// `Ptr` dereferences to an [`Unpin`] type, which cancels the pinning guarantees.
|
||||
///
|
||||
/// # Examples
|
||||
///
|
||||
@@ -493,22 +1174,25 @@ impl<P: Deref<Target: Unpin>> Pin<P> {
|
||||
/// use std::pin::Pin;
|
||||
///
|
||||
/// let mut val: u8 = 5;
|
||||
/// // We can pin the value, since it doesn't care about being moved
|
||||
///
|
||||
/// // Since `val` doesn't care about being moved, we can safely create a "facade" `Pin`
|
||||
/// // which will allow `val` to participate in `Pin`-bound apis without checking that
|
||||
/// // pinning guarantees are actually upheld.
|
||||
/// let mut pinned: Pin<&mut u8> = Pin::new(&mut val);
|
||||
/// ```
|
||||
#[inline(always)]
|
||||
#[rustc_const_unstable(feature = "const_pin", issue = "76654")]
|
||||
#[stable(feature = "pin", since = "1.33.0")]
|
||||
pub const fn new(pointer: P) -> Pin<P> {
|
||||
pub const fn new(pointer: Ptr) -> Pin<Ptr> {
|
||||
// SAFETY: the value pointed to is `Unpin`, and so has no requirements
|
||||
// around pinning.
|
||||
unsafe { Pin::new_unchecked(pointer) }
|
||||
}
|
||||
|
||||
/// Unwraps this `Pin<P>` returning the underlying pointer.
|
||||
/// Unwraps this `Pin<Ptr>`, returning the underlying pointer.
|
||||
///
|
||||
/// This requires that the data inside this `Pin` implements [`Unpin`] so that we
|
||||
/// can ignore the pinning invariants when unwrapping it.
|
||||
/// Doing this operation safely requires that the data pointed at by this pinning pointer
|
||||
/// implemts [`Unpin`] so that we can ignore the pinning invariants when unwrapping it.
|
||||
///
|
||||
/// # Examples
|
||||
///
|
||||
@@ -517,46 +1201,54 @@ pub const fn new(pointer: P) -> Pin<P> {
|
||||
///
|
||||
/// let mut val: u8 = 5;
|
||||
/// let pinned: Pin<&mut u8> = Pin::new(&mut val);
|
||||
/// // Unwrap the pin to get a reference to the value
|
||||
///
|
||||
/// // Unwrap the pin to get the underlying mutable reference to the value. We can do
|
||||
/// // this because `val` doesn't care about being moved, so the `Pin` was just
|
||||
/// // a "facade" anyway.
|
||||
/// let r = Pin::into_inner(pinned);
|
||||
/// assert_eq!(*r, 5);
|
||||
/// ```
|
||||
#[inline(always)]
|
||||
#[rustc_const_unstable(feature = "const_pin", issue = "76654")]
|
||||
#[stable(feature = "pin_into_inner", since = "1.39.0")]
|
||||
pub const fn into_inner(pin: Pin<P>) -> P {
|
||||
pub const fn into_inner(pin: Pin<Ptr>) -> Ptr {
|
||||
pin.pointer
|
||||
}
|
||||
}
|
||||
|
||||
impl<P: Deref> Pin<P> {
|
||||
/// Construct a new `Pin<P>` around a reference to some data of a type that
|
||||
/// may or may not implement `Unpin`.
|
||||
impl<Ptr: Deref> Pin<Ptr> {
|
||||
/// Construct a new `Pin<Ptr>` around a reference to some data of a type that
|
||||
/// may or may not implement [`Unpin`].
|
||||
///
|
||||
/// If `pointer` dereferences to an `Unpin` type, `Pin::new` should be used
|
||||
/// If `pointer` dereferences to an [`Unpin`] type, [`Pin::new`] should be used
|
||||
/// instead.
|
||||
///
|
||||
/// # Safety
|
||||
///
|
||||
/// This constructor is unsafe because we cannot guarantee that the data
|
||||
/// pointed to by `pointer` is pinned, meaning that the data will not be moved or
|
||||
/// its storage invalidated until it gets dropped. If the constructed `Pin<P>` does
|
||||
/// not guarantee that the data `P` points to is pinned, that is a violation of
|
||||
/// the API contract and may lead to undefined behavior in later (safe) operations.
|
||||
/// pointed to by `pointer` is pinned. At its core, pinning a value means making the
|
||||
/// guarantee that the value's data will not be moved nor have its storage invalidated until
|
||||
/// it gets dropped. For a more thorough explanation of pinning, see the [`pin` module docs].
|
||||
///
|
||||
/// By using this method, you are making a promise about the `P::Deref` and
|
||||
/// `P::DerefMut` implementations, if they exist. Most importantly, they
|
||||
/// If the caller that is constructing this `Pin<Ptr>` does not ensure that the data `Ptr`
|
||||
/// points to is pinned, that is a violation of the API contract and may lead to undefined
|
||||
/// behavior in later (even safe) operations.
|
||||
///
|
||||
/// By using this method, you are also making a promise about the [`Deref`] and
|
||||
/// [`DerefMut`] implementations of `Ptr`, if they exist. Most importantly, they
|
||||
/// must not move out of their `self` arguments: `Pin::as_mut` and `Pin::as_ref`
|
||||
/// will call `DerefMut::deref_mut` and `Deref::deref` *on the pinned pointer*
|
||||
/// will call `DerefMut::deref_mut` and `Deref::deref` *on the pointer type `Ptr`*
|
||||
/// and expect these methods to uphold the pinning invariants.
|
||||
/// Moreover, by calling this method you promise that the reference `P`
|
||||
/// Moreover, by calling this method you promise that the reference `Ptr`
|
||||
/// dereferences to will not be moved out of again; in particular, it
|
||||
/// must not be possible to obtain a `&mut P::Target` and then
|
||||
/// must not be possible to obtain a `&mut Ptr::Target` and then
|
||||
/// move out of that reference (using, for example [`mem::swap`]).
|
||||
///
|
||||
/// For example, calling `Pin::new_unchecked` on an `&'a mut T` is unsafe because
|
||||
/// while you are able to pin it for the given lifetime `'a`, you have no control
|
||||
/// over whether it is kept pinned once `'a` ends:
|
||||
/// over whether it is kept pinned once `'a` ends, and therefore cannot uphold the
|
||||
/// guarantee that a value, once pinned, remains pinned until it is dropped:
|
||||
///
|
||||
/// ```
|
||||
/// use std::mem;
|
||||
/// use std::pin::Pin;
|
||||
@@ -583,12 +1275,14 @@ impl<P: Deref> Pin<P> {
|
||||
/// use std::pin::Pin;
|
||||
///
|
||||
/// fn move_pinned_rc<T>(mut x: Rc<T>) {
|
||||
/// let pinned = unsafe { Pin::new_unchecked(Rc::clone(&x)) };
|
||||
/// // This should mean the pointee can never move again.
|
||||
/// let pin = unsafe { Pin::new_unchecked(Rc::clone(&x)) };
|
||||
/// {
|
||||
/// let p: Pin<&T> = pinned.as_ref();
|
||||
/// // This should mean the pointee can never move again.
|
||||
/// let p: Pin<&T> = pin.as_ref();
|
||||
/// // ...
|
||||
/// }
|
||||
/// drop(pinned);
|
||||
/// drop(pin);
|
||||
///
|
||||
/// let content = Rc::get_mut(&mut x).unwrap(); // Potential UB down the road ⚠️
|
||||
/// // Now, if `x` was the only reference, we have a mutable reference to
|
||||
/// // data that we pinned above, which we could use to move it as we have
|
||||
@@ -649,15 +1343,16 @@ impl<P: Deref> Pin<P> {
|
||||
/// ```
|
||||
///
|
||||
/// [`mem::swap`]: crate::mem::swap
|
||||
/// [`pin` module docs]: self
|
||||
#[lang = "new_unchecked"]
|
||||
#[inline(always)]
|
||||
#[rustc_const_unstable(feature = "const_pin", issue = "76654")]
|
||||
#[stable(feature = "pin", since = "1.33.0")]
|
||||
pub const unsafe fn new_unchecked(pointer: P) -> Pin<P> {
|
||||
pub const unsafe fn new_unchecked(pointer: Ptr) -> Pin<Ptr> {
|
||||
Pin { pointer }
|
||||
}
|
||||
|
||||
/// Gets a pinned shared reference from this pinned pointer.
|
||||
/// Gets a shared reference to the pinned value this [`Pin`] points to.
|
||||
///
|
||||
/// This is a generic method to go from `&Pin<Pointer<T>>` to `Pin<&T>`.
|
||||
/// It is safe because, as part of the contract of `Pin::new_unchecked`,
|
||||
@@ -666,34 +1361,39 @@ impl<P: Deref> Pin<P> {
|
||||
/// ruled out by the contract of `Pin::new_unchecked`.
|
||||
#[stable(feature = "pin", since = "1.33.0")]
|
||||
#[inline(always)]
|
||||
pub fn as_ref(&self) -> Pin<&P::Target> {
|
||||
pub fn as_ref(&self) -> Pin<&Ptr::Target> {
|
||||
// SAFETY: see documentation on this function
|
||||
unsafe { Pin::new_unchecked(&*self.pointer) }
|
||||
}
|
||||
|
||||
/// Unwraps this `Pin<P>` returning the underlying pointer.
|
||||
/// Unwraps this `Pin<Ptr>`, returning the underlying `Ptr`.
|
||||
///
|
||||
/// # Safety
|
||||
///
|
||||
/// This function is unsafe. You must guarantee that you will continue to
|
||||
/// treat the pointer `P` as pinned after you call this function, so that
|
||||
/// treat the pointer `Ptr` as pinned after you call this function, so that
|
||||
/// the invariants on the `Pin` type can be upheld. If the code using the
|
||||
/// resulting `P` does not continue to maintain the pinning invariants that
|
||||
/// resulting `Ptr` does not continue to maintain the pinning invariants that
|
||||
/// is a violation of the API contract and may lead to undefined behavior in
|
||||
/// later (safe) operations.
|
||||
///
|
||||
/// Note that you must be able to guarantee that the data pointed to by `Ptr`
|
||||
/// will be treated as pinned all the way until its `drop` handler is complete!
|
||||
///
|
||||
/// *For more information, see the [`pin` module docs][self]*
|
||||
///
|
||||
/// If the underlying data is [`Unpin`], [`Pin::into_inner`] should be used
|
||||
/// instead.
|
||||
#[inline(always)]
|
||||
#[rustc_const_unstable(feature = "const_pin", issue = "76654")]
|
||||
#[stable(feature = "pin_into_inner", since = "1.39.0")]
|
||||
pub const unsafe fn into_inner_unchecked(pin: Pin<P>) -> P {
|
||||
pub const unsafe fn into_inner_unchecked(pin: Pin<Ptr>) -> Ptr {
|
||||
pin.pointer
|
||||
}
|
||||
}
|
||||
|
||||
impl<P: DerefMut> Pin<P> {
|
||||
/// Gets a pinned mutable reference from this pinned pointer.
|
||||
impl<Ptr: DerefMut> Pin<Ptr> {
|
||||
/// Gets a mutable reference to the pinned value this `Pin<Ptr>` points to.
|
||||
///
|
||||
/// This is a generic method to go from `&mut Pin<Pointer<T>>` to `Pin<&mut T>`.
|
||||
/// It is safe because, as part of the contract of `Pin::new_unchecked`,
|
||||
@@ -701,7 +1401,8 @@ impl<P: DerefMut> Pin<P> {
|
||||
/// "Malicious" implementations of `Pointer::DerefMut` are likewise
|
||||
/// ruled out by the contract of `Pin::new_unchecked`.
|
||||
///
|
||||
/// This method is useful when doing multiple calls to functions that consume the pinned type.
|
||||
/// This method is useful when doing multiple calls to functions that consume the
|
||||
/// pinning pointer.
|
||||
///
|
||||
/// # Example
|
||||
///
|
||||
@@ -723,15 +1424,17 @@ impl<P: DerefMut> Pin<P> {
|
||||
/// ```
|
||||
#[stable(feature = "pin", since = "1.33.0")]
|
||||
#[inline(always)]
|
||||
pub fn as_mut(&mut self) -> Pin<&mut P::Target> {
|
||||
pub fn as_mut(&mut self) -> Pin<&mut Ptr::Target> {
|
||||
// SAFETY: see documentation on this function
|
||||
unsafe { Pin::new_unchecked(&mut *self.pointer) }
|
||||
}
|
||||
|
||||
/// Assigns a new value to the memory behind the pinned reference.
|
||||
/// Assigns a new value to the memory location pointed to by the `Pin<Ptr>`.
|
||||
///
|
||||
/// This overwrites pinned data, but that is okay: its destructor gets
|
||||
/// run before being overwritten, so no pinning guarantee is violated.
|
||||
/// This overwrites pinned data, but that is okay: the original pinned value's destructor gets
|
||||
/// run before being overwritten and the new value is also a valid value of the same type, so
|
||||
/// no pinning invariant is violated. See [the `pin` module documentation][subtle-details]
|
||||
/// for more information on how this upholds the pinning invariants.
|
||||
///
|
||||
/// # Example
|
||||
///
|
||||
@@ -741,14 +1444,16 @@ pub fn as_mut(&mut self) -> Pin<&mut P::Target> {
|
||||
/// let mut val: u8 = 5;
|
||||
/// let mut pinned: Pin<&mut u8> = Pin::new(&mut val);
|
||||
/// println!("{}", pinned); // 5
|
||||
/// pinned.as_mut().set(10);
|
||||
/// pinned.set(10);
|
||||
/// println!("{}", pinned); // 10
|
||||
/// ```
|
||||
///
|
||||
/// [subtle-details]: self#subtle-details-and-the-drop-guarantee
|
||||
#[stable(feature = "pin", since = "1.33.0")]
|
||||
#[inline(always)]
|
||||
pub fn set(&mut self, value: P::Target)
|
||||
pub fn set(&mut self, value: Ptr::Target)
|
||||
where
|
||||
P::Target: Sized,
|
||||
Ptr::Target: Sized,
|
||||
{
|
||||
*(self.pointer) = value;
|
||||
}
|
||||
@@ -790,15 +1495,15 @@ pub unsafe fn map_unchecked<U, F>(self, func: F) -> Pin<&'a U>
|
||||
/// It may seem like there is an issue here with interior mutability: in fact,
|
||||
/// it *is* possible to move a `T` out of a `&RefCell<T>`. However, this is
|
||||
/// not a problem as long as there does not also exist a `Pin<&T>` pointing
|
||||
/// to the same data, and `RefCell<T>` does not let you create a pinned reference
|
||||
/// to its contents. See the discussion on ["pinning projections"] for further
|
||||
/// details.
|
||||
/// to the inner `T` inside the `RefCell`, and `RefCell<T>` does not let you get a
|
||||
/// `Pin<&T>` pointer to its contents. See the discussion on ["pinning projections"]
|
||||
/// for further details.
|
||||
///
|
||||
/// Note: `Pin` also implements `Deref` to the target, which can be used
|
||||
/// to access the inner value. However, `Deref` only provides a reference
|
||||
/// that lives for as long as the borrow of the `Pin`, not the lifetime of
|
||||
/// the `Pin` itself. This method allows turning the `Pin` into a reference
|
||||
/// with the same lifetime as the original `Pin`.
|
||||
/// the reference contained in the `Pin`. This method allows turning the `Pin` into a reference
|
||||
/// with the same lifetime as the reference it wraps.
|
||||
///
|
||||
/// ["pinning projections"]: self#projections-and-structural-pinning
|
||||
#[inline(always)]
|
||||
@@ -891,9 +1596,9 @@ pub unsafe fn map_unchecked_mut<U, F>(self, func: F) -> Pin<&'a mut U>
|
||||
}
|
||||
|
||||
impl<T: ?Sized> Pin<&'static T> {
|
||||
/// Get a pinned reference from a static reference.
|
||||
/// Get a pinning reference from a `&'static` reference.
|
||||
///
|
||||
/// This is safe, because `T` is borrowed for the `'static` lifetime, which
|
||||
/// This is safe because `T` is borrowed immutably for the `'static` lifetime, which
|
||||
/// never ends.
|
||||
#[stable(feature = "pin_static_ref", since = "1.61.0")]
|
||||
#[rustc_const_unstable(feature = "const_pin", issue = "76654")]
|
||||
@@ -904,49 +1609,50 @@ pub const fn static_ref(r: &'static T) -> Pin<&'static T> {
|
||||
}
|
||||
}
|
||||
|
||||
impl<'a, P: DerefMut> Pin<&'a mut Pin<P>> {
|
||||
/// Gets a pinned mutable reference from this nested pinned pointer.
|
||||
impl<'a, Ptr: DerefMut> Pin<&'a mut Pin<Ptr>> {
|
||||
/// Gets `Pin<&mut T>` to the underlying pinned value from this nested `Pin`-pointer.
|
||||
///
|
||||
/// This is a generic method to go from `Pin<&mut Pin<Pointer<T>>>` to `Pin<&mut T>`. It is
|
||||
/// safe because the existence of a `Pin<Pointer<T>>` ensures that the pointee, `T`, cannot
|
||||
/// move in the future, and this method does not enable the pointee to move. "Malicious"
|
||||
/// implementations of `P::DerefMut` are likewise ruled out by the contract of
|
||||
/// implementations of `Ptr::DerefMut` are likewise ruled out by the contract of
|
||||
/// `Pin::new_unchecked`.
|
||||
#[unstable(feature = "pin_deref_mut", issue = "86918")]
|
||||
#[must_use = "`self` will be dropped if the result is not used"]
|
||||
#[inline(always)]
|
||||
pub fn as_deref_mut(self) -> Pin<&'a mut P::Target> {
|
||||
pub fn as_deref_mut(self) -> Pin<&'a mut Ptr::Target> {
|
||||
// SAFETY: What we're asserting here is that going from
|
||||
//
|
||||
// Pin<&mut Pin<P>>
|
||||
// Pin<&mut Pin<Ptr>>
|
||||
//
|
||||
// to
|
||||
//
|
||||
// Pin<&mut P::Target>
|
||||
// Pin<&mut Ptr::Target>
|
||||
//
|
||||
// is safe.
|
||||
//
|
||||
// We need to ensure that two things hold for that to be the case:
|
||||
//
|
||||
// 1) Once we give out a `Pin<&mut P::Target>`, an `&mut P::Target` will not be given out.
|
||||
// 2) By giving out a `Pin<&mut P::Target>`, we do not risk of violating `Pin<&mut Pin<P>>`
|
||||
// 1) Once we give out a `Pin<&mut Ptr::Target>`, an `&mut Ptr::Target` will not be given out.
|
||||
// 2) By giving out a `Pin<&mut Ptr::Target>`, we do not risk of violating
|
||||
// `Pin<&mut Pin<Ptr>>`
|
||||
//
|
||||
// The existence of `Pin<P>` is sufficient to guarantee #1: since we already have a
|
||||
// `Pin<P>`, it must already uphold the pinning guarantees, which must mean that
|
||||
// `Pin<&mut P::Target>` does as well, since `Pin::as_mut` is safe. We do not have to rely
|
||||
// on the fact that P is _also_ pinned.
|
||||
// The existence of `Pin<Ptr>` is sufficient to guarantee #1: since we already have a
|
||||
// `Pin<Ptr>`, it must already uphold the pinning guarantees, which must mean that
|
||||
// `Pin<&mut Ptr::Target>` does as well, since `Pin::as_mut` is safe. We do not have to rely
|
||||
// on the fact that `Ptr` is _also_ pinned.
|
||||
//
|
||||
// For #2, we need to ensure that code given a `Pin<&mut P::Target>` cannot cause the
|
||||
// `Pin<P>` to move? That is not possible, since `Pin<&mut P::Target>` no longer retains
|
||||
// any access to the `P` itself, much less the `Pin<P>`.
|
||||
// For #2, we need to ensure that code given a `Pin<&mut Ptr::Target>` cannot cause the
|
||||
// `Pin<Ptr>` to move? That is not possible, since `Pin<&mut Ptr::Target>` no longer retains
|
||||
// any access to the `Ptr` itself, much less the `Pin<Ptr>`.
|
||||
unsafe { self.get_unchecked_mut() }.as_mut()
|
||||
}
|
||||
}
|
||||
|
||||
impl<T: ?Sized> Pin<&'static mut T> {
|
||||
/// Get a pinned mutable reference from a static mutable reference.
|
||||
/// Get a pinning mutable reference from a static mutable reference.
|
||||
///
|
||||
/// This is safe, because `T` is borrowed for the `'static` lifetime, which
|
||||
/// This is safe because `T` is borrowed for the `'static` lifetime, which
|
||||
/// never ends.
|
||||
#[stable(feature = "pin_static_ref", since = "1.61.0")]
|
||||
#[rustc_const_unstable(feature = "const_pin", issue = "76654")]
|
||||
@@ -958,39 +1664,39 @@ pub const fn static_mut(r: &'static mut T) -> Pin<&'static mut T> {
|
||||
}
|
||||
|
||||
#[stable(feature = "pin", since = "1.33.0")]
|
||||
impl<P: Deref> Deref for Pin<P> {
|
||||
type Target = P::Target;
|
||||
fn deref(&self) -> &P::Target {
|
||||
impl<Ptr: Deref> Deref for Pin<Ptr> {
|
||||
type Target = Ptr::Target;
|
||||
fn deref(&self) -> &Ptr::Target {
|
||||
Pin::get_ref(Pin::as_ref(self))
|
||||
}
|
||||
}
|
||||
|
||||
#[stable(feature = "pin", since = "1.33.0")]
|
||||
impl<P: DerefMut<Target: Unpin>> DerefMut for Pin<P> {
|
||||
fn deref_mut(&mut self) -> &mut P::Target {
|
||||
impl<Ptr: DerefMut<Target: Unpin>> DerefMut for Pin<Ptr> {
|
||||
fn deref_mut(&mut self) -> &mut Ptr::Target {
|
||||
Pin::get_mut(Pin::as_mut(self))
|
||||
}
|
||||
}
|
||||
|
||||
#[unstable(feature = "receiver_trait", issue = "none")]
|
||||
impl<P: Receiver> Receiver for Pin<P> {}
|
||||
impl<Ptr: Receiver> Receiver for Pin<Ptr> {}
|
||||
|
||||
#[stable(feature = "pin", since = "1.33.0")]
|
||||
impl<P: fmt::Debug> fmt::Debug for Pin<P> {
|
||||
impl<Ptr: fmt::Debug> fmt::Debug for Pin<Ptr> {
|
||||
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
|
||||
fmt::Debug::fmt(&self.pointer, f)
|
||||
}
|
||||
}
|
||||
|
||||
#[stable(feature = "pin", since = "1.33.0")]
|
||||
impl<P: fmt::Display> fmt::Display for Pin<P> {
|
||||
impl<Ptr: fmt::Display> fmt::Display for Pin<Ptr> {
|
||||
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
|
||||
fmt::Display::fmt(&self.pointer, f)
|
||||
}
|
||||
}
|
||||
|
||||
#[stable(feature = "pin", since = "1.33.0")]
|
||||
impl<P: fmt::Pointer> fmt::Pointer for Pin<P> {
|
||||
impl<Ptr: fmt::Pointer> fmt::Pointer for Pin<Ptr> {
|
||||
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
|
||||
fmt::Pointer::fmt(&self.pointer, f)
|
||||
}
|
||||
@@ -1002,10 +1708,10 @@ fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
|
||||
// for other reasons, though, so we just need to take care not to allow such
|
||||
// impls to land in std.
|
||||
#[stable(feature = "pin", since = "1.33.0")]
|
||||
impl<P, U> CoerceUnsized<Pin<U>> for Pin<P> where P: CoerceUnsized<U> {}
|
||||
impl<Ptr, U> CoerceUnsized<Pin<U>> for Pin<Ptr> where Ptr: CoerceUnsized<U> {}
|
||||
|
||||
#[stable(feature = "pin", since = "1.33.0")]
|
||||
impl<P, U> DispatchFromDyn<Pin<U>> for Pin<P> where P: DispatchFromDyn<U> {}
|
||||
impl<Ptr, U> DispatchFromDyn<Pin<U>> for Pin<Ptr> where Ptr: DispatchFromDyn<U> {}
|
||||
|
||||
/// Constructs a <code>[Pin]<[&mut] T></code>, by pinning a `value: T` locally.
|
||||
///
|
||||
|
||||
@@ -33,7 +33,6 @@
|
||||
"tests/ui/macros/macro-expanded-include/file.txt", // testing including data with the include macros
|
||||
"tests/ui/macros/not-utf8.bin", // testing including data with the include macros
|
||||
"tests/ui/macros/syntax-extension-source-utils-files/includeme.fragment", // more include
|
||||
"tests/ui/unused-crate-deps/test.mk", // why would you use make
|
||||
"tests/ui/proc-macro/auxiliary/included-file.txt", // more include
|
||||
"tests/ui/invalid/foo.natvis.xml", // sample debugger visualizer
|
||||
];
|
||||
|
||||
@@ -33,11 +33,13 @@ LL | fn main<A: TraitWAssocConst<A=32>>() {
|
||||
= note: see issue #92827 <https://github.com/rust-lang/rust/issues/92827> for more information
|
||||
= help: add `#![feature(associated_const_equality)]` to the crate attributes to enable
|
||||
|
||||
error[E0562]: `impl Trait` only allowed in function and inherent method argument and return types, not in impl headers
|
||||
error[E0562]: `impl Trait` is not allowed in impl headers
|
||||
--> $DIR/issue-105330.rs:6:27
|
||||
|
|
||||
LL | impl TraitWAssocConst for impl Demo {
|
||||
| ^^^^^^^^^
|
||||
|
|
||||
= note: `impl Trait` is only allowed in arguments and return types of functions and methods
|
||||
|
||||
error[E0131]: `main` function is not allowed to have generic parameters
|
||||
--> $DIR/issue-105330.rs:15:8
|
||||
|
||||
@@ -13,7 +13,7 @@ note: required because it appears within the type `Sleep`
|
||||
|
|
||||
LL | struct Sleep(std::marker::PhantomPinned);
|
||||
| ^^^^^
|
||||
note: required by a bound in `Pin::<P>::new`
|
||||
note: required by a bound in `Pin::<Ptr>::new`
|
||||
--> $SRC_DIR/core/src/pin.rs:LL:COL
|
||||
|
||||
error: aborting due to 1 previous error
|
||||
|
||||
@@ -1,4 +1,4 @@
|
||||
error[E0133]: call to unsafe function `Pin::<P>::new_unchecked` is unsafe and requires unsafe function or block
|
||||
error[E0133]: call to unsafe function `Pin::<Ptr>::new_unchecked` is unsafe and requires unsafe function or block
|
||||
--> $DIR/coerce-unsafe-closure-to-unsafe-fn-ptr.rs:2:31
|
||||
|
|
||||
LL | let _: unsafe fn() = || { ::std::pin::Pin::new_unchecked(&0_u8); };
|
||||
|
||||
@@ -0,0 +1,16 @@
|
||||
#![feature(dyn_star)]
|
||||
//~^ WARN the feature `dyn_star` is incomplete and may not be safe to use and/or cause compiler crashes
|
||||
|
||||
union Union {
|
||||
x: usize,
|
||||
}
|
||||
|
||||
trait Trait {}
|
||||
impl Trait for Union {}
|
||||
|
||||
fn bar(_: dyn* Trait) {}
|
||||
|
||||
fn main() {
|
||||
bar(Union { x: 0usize });
|
||||
//~^ ERROR `Union` needs to have the same ABI as a pointer
|
||||
}
|
||||
@@ -0,0 +1,20 @@
|
||||
warning: the feature `dyn_star` is incomplete and may not be safe to use and/or cause compiler crashes
|
||||
--> $DIR/union.rs:1:12
|
||||
|
|
||||
LL | #![feature(dyn_star)]
|
||||
| ^^^^^^^^
|
||||
|
|
||||
= note: see issue #102425 <https://github.com/rust-lang/rust/issues/102425> for more information
|
||||
= note: `#[warn(incomplete_features)]` on by default
|
||||
|
||||
error[E0277]: `Union` needs to have the same ABI as a pointer
|
||||
--> $DIR/union.rs:14:9
|
||||
|
|
||||
LL | bar(Union { x: 0usize });
|
||||
| ^^^^^^^^^^^^^^^^^^^ `Union` needs to be a pointer-like type
|
||||
|
|
||||
= help: the trait `PointerLike` is not implemented for `Union`
|
||||
|
||||
error: aborting due to 1 previous error; 1 warning emitted
|
||||
|
||||
For more information about this error, try `rustc --explain E0277`.
|
||||
@@ -54,20 +54,20 @@ fn _rpit_dyn() -> Box<dyn Tr1<As1: Copy>> { Box::new(S1) }
|
||||
|
||||
const _cdef: impl Tr1<As1: Copy> = S1;
|
||||
//~^ ERROR associated type bounds are unstable
|
||||
//~| ERROR `impl Trait` only allowed in function and inherent method argument and return types
|
||||
//~| ERROR `impl Trait` is not allowed in const types
|
||||
// FIXME: uncomment when `impl_trait_in_bindings` feature is fixed.
|
||||
// const _cdef_dyn: &dyn Tr1<As1: Copy> = &S1;
|
||||
|
||||
static _sdef: impl Tr1<As1: Copy> = S1;
|
||||
//~^ ERROR associated type bounds are unstable
|
||||
//~| ERROR `impl Trait` only allowed in function and inherent method argument and return types
|
||||
//~| ERROR `impl Trait` is not allowed in static types
|
||||
// FIXME: uncomment when `impl_trait_in_bindings` feature is fixed.
|
||||
// static _sdef_dyn: &dyn Tr1<As1: Copy> = &S1;
|
||||
|
||||
fn main() {
|
||||
let _: impl Tr1<As1: Copy> = S1;
|
||||
//~^ ERROR associated type bounds are unstable
|
||||
//~| ERROR `impl Trait` only allowed in function and inherent method argument and return types
|
||||
//~| ERROR `impl Trait` is not allowed in the type of variable bindings
|
||||
// FIXME: uncomment when `impl_trait_in_bindings` feature is fixed.
|
||||
// let _: &dyn Tr1<As1: Copy> = &S1;
|
||||
}
|
||||
|
||||
@@ -115,23 +115,29 @@ LL | let _: impl Tr1<As1: Copy> = S1;
|
||||
= note: see issue #52662 <https://github.com/rust-lang/rust/issues/52662> for more information
|
||||
= help: add `#![feature(associated_type_bounds)]` to the crate attributes to enable
|
||||
|
||||
error[E0562]: `impl Trait` only allowed in function and inherent method argument and return types, not in const types
|
||||
error[E0562]: `impl Trait` is not allowed in const types
|
||||
--> $DIR/feature-gate-associated_type_bounds.rs:55:14
|
||||
|
|
||||
LL | const _cdef: impl Tr1<As1: Copy> = S1;
|
||||
| ^^^^^^^^^^^^^^^^^^^
|
||||
|
|
||||
= note: `impl Trait` is only allowed in arguments and return types of functions and methods
|
||||
|
||||
error[E0562]: `impl Trait` only allowed in function and inherent method argument and return types, not in const types
|
||||
error[E0562]: `impl Trait` is not allowed in static types
|
||||
--> $DIR/feature-gate-associated_type_bounds.rs:61:15
|
||||
|
|
||||
LL | static _sdef: impl Tr1<As1: Copy> = S1;
|
||||
| ^^^^^^^^^^^^^^^^^^^
|
||||
|
|
||||
= note: `impl Trait` is only allowed in arguments and return types of functions and methods
|
||||
|
||||
error[E0562]: `impl Trait` only allowed in function and inherent method argument and return types, not in variable bindings
|
||||
error[E0562]: `impl Trait` is not allowed in the type of variable bindings
|
||||
--> $DIR/feature-gate-associated_type_bounds.rs:68:12
|
||||
|
|
||||
LL | let _: impl Tr1<As1: Copy> = S1;
|
||||
| ^^^^^^^^^^^^^^^^^^^
|
||||
|
|
||||
= note: `impl Trait` is only allowed in arguments and return types of functions and methods
|
||||
|
||||
error[E0277]: the trait bound `<<Self as _Tr3>::A as Iterator>::Item: Copy` is not satisfied
|
||||
--> $DIR/feature-gate-associated_type_bounds.rs:12:28
|
||||
|
||||
@@ -1,6 +1,6 @@
|
||||
fn f() -> impl Fn() -> impl Sized { || () }
|
||||
//~^ ERROR `impl Trait` only allowed in function and inherent method argument and return types, not in `Fn` trait return
|
||||
//~^ ERROR `impl Trait` is not allowed in the return type of `Fn` trait bounds
|
||||
fn g() -> &'static dyn Fn() -> impl Sized { &|| () }
|
||||
//~^ ERROR `impl Trait` only allowed in function and inherent method argument and return types, not in `Fn` trait return
|
||||
//~^ ERROR `impl Trait` is not allowed in the return type of `Fn` trait bounds
|
||||
|
||||
fn main() {}
|
||||
|
||||
@@ -1,18 +1,20 @@
|
||||
error[E0562]: `impl Trait` only allowed in function and inherent method argument and return types, not in `Fn` trait return types
|
||||
error[E0562]: `impl Trait` is not allowed in the return type of `Fn` trait bounds
|
||||
--> $DIR/feature-gate-impl_trait_in_fn_trait_return.rs:1:24
|
||||
|
|
||||
LL | fn f() -> impl Fn() -> impl Sized { || () }
|
||||
| ^^^^^^^^^^
|
||||
|
|
||||
= note: `impl Trait` is only allowed in arguments and return types of functions and methods
|
||||
= note: see issue #99697 <https://github.com/rust-lang/rust/issues/99697> for more information
|
||||
= help: add `#![feature(impl_trait_in_fn_trait_return)]` to the crate attributes to enable
|
||||
|
||||
error[E0562]: `impl Trait` only allowed in function and inherent method argument and return types, not in `Fn` trait return types
|
||||
error[E0562]: `impl Trait` is not allowed in the return type of `Fn` trait bounds
|
||||
--> $DIR/feature-gate-impl_trait_in_fn_trait_return.rs:3:32
|
||||
|
|
||||
LL | fn g() -> &'static dyn Fn() -> impl Sized { &|| () }
|
||||
| ^^^^^^^^^^
|
||||
|
|
||||
= note: `impl Trait` is only allowed in arguments and return types of functions and methods
|
||||
= note: see issue #99697 <https://github.com/rust-lang/rust/issues/99697> for more information
|
||||
= help: add `#![feature(impl_trait_in_fn_trait_return)]` to the crate attributes to enable
|
||||
|
||||
|
||||
@@ -2,6 +2,6 @@
|
||||
|
||||
fn main() {
|
||||
let x: Option<impl Debug> = Some(44_u32);
|
||||
//~^ `impl Trait` only allowed in function and inherent method argument and return types
|
||||
//~^ `impl Trait` is not allowed in the type of variable bindings
|
||||
println!("{:?}", x);
|
||||
}
|
||||
|
||||
@@ -1,8 +1,10 @@
|
||||
error[E0562]: `impl Trait` only allowed in function and inherent method argument and return types, not in variable bindings
|
||||
error[E0562]: `impl Trait` is not allowed in the type of variable bindings
|
||||
--> $DIR/issue-54600.rs:4:19
|
||||
|
|
||||
LL | let x: Option<impl Debug> = Some(44_u32);
|
||||
| ^^^^^^^^^^
|
||||
|
|
||||
= note: `impl Trait` is only allowed in arguments and return types of functions and methods
|
||||
|
||||
error: aborting due to 1 previous error
|
||||
|
||||
|
||||
@@ -3,5 +3,5 @@
|
||||
fn main() {
|
||||
let i: i32 = 0;
|
||||
let j: &impl Add = &i;
|
||||
//~^ `impl Trait` only allowed in function and inherent method argument and return types
|
||||
//~^ `impl Trait` is not allowed in the type of variable bindings
|
||||
}
|
||||
|
||||
@@ -1,8 +1,10 @@
|
||||
error[E0562]: `impl Trait` only allowed in function and inherent method argument and return types, not in variable bindings
|
||||
error[E0562]: `impl Trait` is not allowed in the type of variable bindings
|
||||
--> $DIR/issue-54840.rs:5:13
|
||||
|
|
||||
LL | let j: &impl Add = &i;
|
||||
| ^^^^^^^^
|
||||
|
|
||||
= note: `impl Trait` is only allowed in arguments and return types of functions and methods
|
||||
|
||||
error: aborting due to 1 previous error
|
||||
|
||||
|
||||
@@ -8,5 +8,5 @@ fn mk_gen() -> impl Coroutine<Return=!, Yield=()> {
|
||||
|
||||
fn main() {
|
||||
let gens: [impl Coroutine<Return=!, Yield=()>;2] = [ mk_gen(), mk_gen() ];
|
||||
//~^ `impl Trait` only allowed in function and inherent method argument and return types
|
||||
//~^ `impl Trait` is not allowed in the type of variable bindings
|
||||
}
|
||||
|
||||
@@ -1,8 +1,10 @@
|
||||
error[E0562]: `impl Trait` only allowed in function and inherent method argument and return types, not in variable bindings
|
||||
error[E0562]: `impl Trait` is not allowed in the type of variable bindings
|
||||
--> $DIR/issue-58504.rs:10:16
|
||||
|
|
||||
LL | let gens: [impl Coroutine<Return=!, Yield=()>;2] = [ mk_gen(), mk_gen() ];
|
||||
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
||||
|
|
||||
= note: `impl Trait` is only allowed in arguments and return types of functions and methods
|
||||
|
||||
error: aborting due to 1 previous error
|
||||
|
||||
|
||||
@@ -5,9 +5,9 @@ impl Lam for B {}
|
||||
pub struct Wrap<T>(T);
|
||||
|
||||
const _A: impl Lam = {
|
||||
//~^ `impl Trait` only allowed in function and inherent method argument and return types
|
||||
//~^ `impl Trait` is not allowed in const types
|
||||
let x: Wrap<impl Lam> = Wrap(B);
|
||||
//~^ `impl Trait` only allowed in function and inherent method argument and return types
|
||||
//~^ `impl Trait` is not allowed in the type of variable bindings
|
||||
x.0
|
||||
};
|
||||
|
||||
|
||||
@@ -1,14 +1,18 @@
|
||||
error[E0562]: `impl Trait` only allowed in function and inherent method argument and return types, not in const types
|
||||
error[E0562]: `impl Trait` is not allowed in const types
|
||||
--> $DIR/issue-58956.rs:7:11
|
||||
|
|
||||
LL | const _A: impl Lam = {
|
||||
| ^^^^^^^^
|
||||
|
|
||||
= note: `impl Trait` is only allowed in arguments and return types of functions and methods
|
||||
|
||||
error[E0562]: `impl Trait` only allowed in function and inherent method argument and return types, not in variable bindings
|
||||
error[E0562]: `impl Trait` is not allowed in the type of variable bindings
|
||||
--> $DIR/issue-58956.rs:9:17
|
||||
|
|
||||
LL | let x: Wrap<impl Lam> = Wrap(B);
|
||||
| ^^^^^^^^
|
||||
|
|
||||
= note: `impl Trait` is only allowed in arguments and return types of functions and methods
|
||||
|
||||
error: aborting due to 2 previous errors
|
||||
|
||||
|
||||
@@ -1,4 +1,4 @@
|
||||
fn main() {
|
||||
let x : (impl Copy,) = (true,);
|
||||
//~^ `impl Trait` only allowed in function and inherent method argument and return types
|
||||
//~^ `impl Trait` is not allowed in the type of variable bindings
|
||||
}
|
||||
|
||||
@@ -1,8 +1,10 @@
|
||||
error[E0562]: `impl Trait` only allowed in function and inherent method argument and return types, not in variable bindings
|
||||
error[E0562]: `impl Trait` is not allowed in the type of variable bindings
|
||||
--> $DIR/issue-70971.rs:2:14
|
||||
|
|
||||
LL | let x : (impl Copy,) = (true,);
|
||||
| ^^^^^^^^^
|
||||
|
|
||||
= note: `impl Trait` is only allowed in arguments and return types of functions and methods
|
||||
|
||||
error: aborting due to 1 previous error
|
||||
|
||||
|
||||
@@ -1,7 +1,7 @@
|
||||
struct Bug {
|
||||
V1: [(); {
|
||||
let f: impl core::future::Future<Output = u8> = async { 1 };
|
||||
//~^ `impl Trait` only allowed in function and inherent method argument and return types
|
||||
//~^ `impl Trait` is not allowed in the type of variable bindings
|
||||
//~| expected identifier
|
||||
1
|
||||
}],
|
||||
|
||||
@@ -9,11 +9,13 @@ LL | let f: impl core::future::Future<Output = u8> = async { 1 };
|
||||
= help: pass `--edition 2021` to `rustc`
|
||||
= note: for more on editions, read https://doc.rust-lang.org/edition-guide
|
||||
|
||||
error[E0562]: `impl Trait` only allowed in function and inherent method argument and return types, not in variable bindings
|
||||
error[E0562]: `impl Trait` is not allowed in the type of variable bindings
|
||||
--> $DIR/issue-79099.rs:3:16
|
||||
|
|
||||
LL | let f: impl core::future::Future<Output = u8> = async { 1 };
|
||||
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
||||
|
|
||||
= note: `impl Trait` is only allowed in arguments and return types of functions and methods
|
||||
|
||||
error: aborting due to 2 previous errors
|
||||
|
||||
|
||||
@@ -1,8 +1,8 @@
|
||||
struct Foo<T = impl Copy>(T);
|
||||
//~^ ERROR `impl Trait` only allowed in function and inherent method argument and return types
|
||||
//~^ ERROR `impl Trait` is not allowed in generic parameter defaults
|
||||
|
||||
type Result<T, E = impl std::error::Error> = std::result::Result<T, E>;
|
||||
//~^ ERROR `impl Trait` only allowed in function and inherent method argument and return types
|
||||
//~^ ERROR `impl Trait` is not allowed in generic parameter defaults
|
||||
|
||||
// should not cause ICE
|
||||
fn x() -> Foo {
|
||||
|
||||
@@ -1,14 +1,18 @@
|
||||
error[E0562]: `impl Trait` only allowed in function and inherent method argument and return types, not in generic parameter defaults
|
||||
error[E0562]: `impl Trait` is not allowed in generic parameter defaults
|
||||
--> $DIR/issue-83929-impl-trait-in-generic-default.rs:1:16
|
||||
|
|
||||
LL | struct Foo<T = impl Copy>(T);
|
||||
| ^^^^^^^^^
|
||||
|
|
||||
= note: `impl Trait` is only allowed in arguments and return types of functions and methods
|
||||
|
||||
error[E0562]: `impl Trait` only allowed in function and inherent method argument and return types, not in generic parameter defaults
|
||||
error[E0562]: `impl Trait` is not allowed in generic parameter defaults
|
||||
--> $DIR/issue-83929-impl-trait-in-generic-default.rs:4:20
|
||||
|
|
||||
LL | type Result<T, E = impl std::error::Error> = std::result::Result<T, E>;
|
||||
| ^^^^^^^^^^^^^^^^^^^^^^
|
||||
|
|
||||
= note: `impl Trait` is only allowed in arguments and return types of functions and methods
|
||||
|
||||
error: aborting due to 2 previous errors
|
||||
|
||||
|
||||
@@ -3,7 +3,7 @@ impl Trait for () {}
|
||||
|
||||
fn foo<'a: 'a>() {
|
||||
let _x: impl Trait = ();
|
||||
//~^ `impl Trait` only allowed in function and inherent method argument and return types
|
||||
//~^ `impl Trait` is not allowed in the type of variable bindings
|
||||
}
|
||||
|
||||
fn main() {}
|
||||
|
||||
@@ -1,8 +1,10 @@
|
||||
error[E0562]: `impl Trait` only allowed in function and inherent method argument and return types, not in variable bindings
|
||||
error[E0562]: `impl Trait` is not allowed in the type of variable bindings
|
||||
--> $DIR/issue-84919.rs:5:13
|
||||
|
|
||||
LL | let _x: impl Trait = ();
|
||||
| ^^^^^^^^^^
|
||||
|
|
||||
= note: `impl Trait` is only allowed in arguments and return types of functions and methods
|
||||
|
||||
error: aborting due to 1 previous error
|
||||
|
||||
|
||||
@@ -1,5 +1,5 @@
|
||||
static x: impl Fn(&str) -> Result<&str, ()> = move |source| {
|
||||
//~^ `impl Trait` only allowed in function and inherent method argument and return types
|
||||
//~^ `impl Trait` is not allowed in static types
|
||||
let res = (move |source| Ok(source))(source);
|
||||
let res = res.or((move |source| Ok(source))(source));
|
||||
res
|
||||
|
||||
@@ -1,8 +1,10 @@
|
||||
error[E0562]: `impl Trait` only allowed in function and inherent method argument and return types, not in const types
|
||||
error[E0562]: `impl Trait` is not allowed in static types
|
||||
--> $DIR/issue-86642.rs:1:11
|
||||
|
|
||||
LL | static x: impl Fn(&str) -> Result<&str, ()> = move |source| {
|
||||
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
||||
|
|
||||
= note: `impl Trait` is only allowed in arguments and return types of functions and methods
|
||||
|
||||
error: aborting due to 1 previous error
|
||||
|
||||
|
||||
@@ -14,5 +14,5 @@ pub fn new(_: F) -> Self {
|
||||
|
||||
fn main() {
|
||||
let _do_not_waste: Struct<impl Trait<Output = i32>> = Struct::new(());
|
||||
//~^ `impl Trait` only allowed in function and inherent method argument and return types
|
||||
//~^ `impl Trait` is not allowed in the type of variable bindings
|
||||
}
|
||||
|
||||
@@ -1,8 +1,10 @@
|
||||
error[E0562]: `impl Trait` only allowed in function and inherent method argument and return types, not in variable bindings
|
||||
error[E0562]: `impl Trait` is not allowed in the type of variable bindings
|
||||
--> $DIR/issue-87295.rs:16:31
|
||||
|
|
||||
LL | let _do_not_waste: Struct<impl Trait<Output = i32>> = Struct::new(());
|
||||
| ^^^^^^^^^^^^^^^^^^^^^^^^
|
||||
|
|
||||
= note: `impl Trait` is only allowed in arguments and return types of functions and methods
|
||||
|
||||
error: aborting due to 1 previous error
|
||||
|
||||
|
||||
@@ -9,7 +9,7 @@ fn bad_in_ret_position(x: impl Into<u32>) -> impl Into<impl Debug> { x }
|
||||
|
||||
fn bad_in_fn_syntax(x: fn() -> impl Into<impl Debug>) {}
|
||||
//~^ ERROR nested `impl Trait` is not allowed
|
||||
//~| `impl Trait` only allowed in function and inherent method argument and return types
|
||||
//~| `impl Trait` is not allowed in `fn` pointer
|
||||
|
||||
fn bad_in_arg_position(_: impl Into<impl Debug>) { }
|
||||
//~^ ERROR nested `impl Trait` is not allowed
|
||||
|
||||
@@ -34,11 +34,13 @@ LL | fn bad(x: impl Into<u32>) -> impl Into<impl Debug> { x }
|
||||
| | nested `impl Trait` here
|
||||
| outer `impl Trait`
|
||||
|
||||
error[E0562]: `impl Trait` only allowed in function and inherent method argument and return types, not in `fn` pointer return types
|
||||
error[E0562]: `impl Trait` is not allowed in `fn` pointer return types
|
||||
--> $DIR/nested_impl_trait.rs:10:32
|
||||
|
|
||||
LL | fn bad_in_fn_syntax(x: fn() -> impl Into<impl Debug>) {}
|
||||
| ^^^^^^^^^^^^^^^^^^^^^
|
||||
|
|
||||
= note: `impl Trait` is only allowed in arguments and return types of functions and methods
|
||||
|
||||
error[E0277]: the trait bound `impl Debug: From<impl Into<u32>>` is not satisfied
|
||||
--> $DIR/nested_impl_trait.rs:6:46
|
||||
|
||||
@@ -16,47 +16,47 @@ fn in_adt_in_parameters(_: Vec<impl Debug>) { panic!() }
|
||||
|
||||
// Disallowed
|
||||
fn in_fn_parameter_in_parameters(_: fn(impl Debug)) { panic!() }
|
||||
//~^ ERROR `impl Trait` only allowed in function and inherent method argument and return types
|
||||
//~^ ERROR `impl Trait` is not allowed in `fn` pointer
|
||||
|
||||
// Disallowed
|
||||
fn in_fn_return_in_parameters(_: fn() -> impl Debug) { panic!() }
|
||||
//~^ ERROR `impl Trait` only allowed in function and inherent method argument and return types
|
||||
//~^ ERROR `impl Trait` is not allowed in `fn` pointer
|
||||
|
||||
// Disallowed
|
||||
fn in_fn_parameter_in_return() -> fn(impl Debug) { panic!() }
|
||||
//~^ ERROR `impl Trait` only allowed in function and inherent method argument and return types
|
||||
//~^ ERROR `impl Trait` is not allowed in `fn` pointer
|
||||
|
||||
// Disallowed
|
||||
fn in_fn_return_in_return() -> fn() -> impl Debug { panic!() }
|
||||
//~^ ERROR `impl Trait` only allowed in function and inherent method argument and return types
|
||||
//~^ ERROR `impl Trait` is not allowed in `fn` pointer
|
||||
|
||||
// Disallowed
|
||||
fn in_dyn_Fn_parameter_in_parameters(_: &dyn Fn(impl Debug)) { panic!() }
|
||||
//~^ ERROR `impl Trait` only allowed in function and inherent method argument and return types
|
||||
//~^ ERROR `impl Trait` is not allowed in the parameters of `Fn` trait bounds
|
||||
|
||||
// Disallowed
|
||||
fn in_dyn_Fn_return_in_parameters(_: &dyn Fn() -> impl Debug) { panic!() }
|
||||
//~^ ERROR `impl Trait` only allowed in function and inherent method argument and return types
|
||||
//~^ ERROR `impl Trait` is not allowed in the return type of `Fn` trait bounds
|
||||
|
||||
// Disallowed
|
||||
fn in_dyn_Fn_parameter_in_return() -> &'static dyn Fn(impl Debug) { panic!() }
|
||||
//~^ ERROR `impl Trait` only allowed in function and inherent method argument and return types
|
||||
//~^ ERROR `impl Trait` is not allowed in the parameters of `Fn` trait bounds
|
||||
|
||||
// Allowed
|
||||
fn in_dyn_Fn_return_in_return() -> &'static dyn Fn() -> impl Debug { panic!() }
|
||||
|
||||
// Disallowed
|
||||
fn in_impl_Fn_parameter_in_parameters(_: &impl Fn(impl Debug)) { panic!() }
|
||||
//~^ ERROR `impl Trait` only allowed in function and inherent method argument and return types
|
||||
//~^ ERROR `impl Trait` is not allowed in the parameters of `Fn` trait bounds
|
||||
//~^^ ERROR nested `impl Trait` is not allowed
|
||||
|
||||
// Disallowed
|
||||
fn in_impl_Fn_return_in_parameters(_: &impl Fn() -> impl Debug) { panic!() }
|
||||
//~^ ERROR `impl Trait` only allowed in function and inherent method argument and return types
|
||||
//~^ ERROR `impl Trait` is not allowed in the return type of `Fn` trait bounds
|
||||
|
||||
// Disallowed
|
||||
fn in_impl_Fn_parameter_in_return() -> &'static impl Fn(impl Debug) { panic!() }
|
||||
//~^ ERROR `impl Trait` only allowed in function and inherent method argument and return types
|
||||
//~^ ERROR `impl Trait` is not allowed in the parameters of `Fn` trait bounds
|
||||
//~| ERROR nested `impl Trait` is not allowed
|
||||
|
||||
// Allowed
|
||||
@@ -64,11 +64,11 @@ fn in_impl_Fn_return_in_return() -> &'static impl Fn() -> impl Debug { panic!()
|
||||
|
||||
// Disallowed
|
||||
fn in_Fn_parameter_in_generics<F: Fn(impl Debug)> (_: F) { panic!() }
|
||||
//~^ ERROR `impl Trait` only allowed in function and inherent method argument and return types
|
||||
//~^ ERROR `impl Trait` is not allowed in the parameters of `Fn` trait bounds
|
||||
|
||||
// Disallowed
|
||||
fn in_Fn_return_in_generics<F: Fn() -> impl Debug> (_: F) { panic!() }
|
||||
//~^ ERROR `impl Trait` only allowed in function and inherent method argument and return types
|
||||
//~^ ERROR `impl Trait` is not allowed in the return type of `Fn` trait bounds
|
||||
|
||||
|
||||
// Allowed
|
||||
@@ -81,22 +81,22 @@ fn in_impl_Trait_in_return() -> impl IntoIterator<Item = impl IntoIterator> {
|
||||
|
||||
// Disallowed
|
||||
struct InBraceStructField { x: impl Debug }
|
||||
//~^ ERROR `impl Trait` only allowed in function and inherent method argument and return types
|
||||
//~^ ERROR `impl Trait` is not allowed in field types
|
||||
|
||||
// Disallowed
|
||||
struct InAdtInBraceStructField { x: Vec<impl Debug> }
|
||||
//~^ ERROR `impl Trait` only allowed in function and inherent method argument and return types
|
||||
//~^ ERROR `impl Trait` is not allowed in field types
|
||||
|
||||
// Disallowed
|
||||
struct InTupleStructField(impl Debug);
|
||||
//~^ ERROR `impl Trait` only allowed in function and inherent method argument and return types
|
||||
//~^ ERROR `impl Trait` is not allowed in field types
|
||||
|
||||
// Disallowed
|
||||
enum InEnum {
|
||||
InBraceVariant { x: impl Debug },
|
||||
//~^ ERROR `impl Trait` only allowed in function and inherent method argument and return types
|
||||
//~^ ERROR `impl Trait` is not allowed in field types
|
||||
InTupleVariant(impl Debug),
|
||||
//~^ ERROR `impl Trait` only allowed in function and inherent method argument and return types
|
||||
//~^ ERROR `impl Trait` is not allowed in field types
|
||||
}
|
||||
|
||||
// Allowed
|
||||
@@ -136,10 +136,10 @@ fn in_inherent_impl_return() -> impl Debug { () }
|
||||
// Disallowed
|
||||
extern "C" {
|
||||
fn in_foreign_parameters(_: impl Debug);
|
||||
//~^ ERROR `impl Trait` only allowed in function and inherent method argument and return types
|
||||
//~^ ERROR `impl Trait` is not allowed in `extern fn`
|
||||
|
||||
fn in_foreign_return() -> impl Debug;
|
||||
//~^ ERROR `impl Trait` only allowed in function and inherent method argument and return types
|
||||
//~^ ERROR `impl Trait` is not allowed in `extern fn`
|
||||
}
|
||||
|
||||
// Allowed
|
||||
@@ -155,97 +155,97 @@ extern "C" fn in_extern_fn_return() -> impl Debug {
|
||||
//~^ ERROR `impl Trait` in type aliases is unstable
|
||||
|
||||
type InReturnInTypeAlias<R> = fn() -> impl Debug;
|
||||
//~^ ERROR `impl Trait` only allowed in function and inherent method argument and return types
|
||||
//~^ ERROR `impl Trait` is not allowed in `fn` pointer
|
||||
//~| ERROR `impl Trait` in type aliases is unstable
|
||||
|
||||
// Disallowed in impl headers
|
||||
impl PartialEq<impl Debug> for () {
|
||||
//~^ ERROR `impl Trait` only allowed in function and inherent method argument and return types
|
||||
//~^ ERROR `impl Trait` is not allowed in traits
|
||||
}
|
||||
|
||||
// Disallowed in impl headers
|
||||
impl PartialEq<()> for impl Debug {
|
||||
//~^ ERROR `impl Trait` only allowed in function and inherent method argument and return types
|
||||
//~^ ERROR `impl Trait` is not allowed in impl headers
|
||||
}
|
||||
|
||||
// Disallowed in inherent impls
|
||||
impl impl Debug {
|
||||
//~^ ERROR `impl Trait` only allowed in function and inherent method argument and return types
|
||||
//~^ ERROR `impl Trait` is not allowed in impl headers
|
||||
}
|
||||
|
||||
// Disallowed in inherent impls
|
||||
struct InInherentImplAdt<T> { t: T }
|
||||
impl InInherentImplAdt<impl Debug> {
|
||||
//~^ ERROR `impl Trait` only allowed in function and inherent method argument and return types
|
||||
//~^ ERROR `impl Trait` is not allowed in impl headers
|
||||
}
|
||||
|
||||
// Disallowed in where clauses
|
||||
fn in_fn_where_clause()
|
||||
where impl Debug: Debug
|
||||
//~^ ERROR `impl Trait` only allowed in function and inherent method argument and return types
|
||||
//~^ ERROR `impl Trait` is not allowed in bounds
|
||||
{
|
||||
}
|
||||
|
||||
// Disallowed in where clauses
|
||||
fn in_adt_in_fn_where_clause()
|
||||
where Vec<impl Debug>: Debug
|
||||
//~^ ERROR `impl Trait` only allowed in function and inherent method argument and return types
|
||||
//~^ ERROR `impl Trait` is not allowed in bounds
|
||||
{
|
||||
}
|
||||
|
||||
// Disallowed
|
||||
fn in_trait_parameter_in_fn_where_clause<T>()
|
||||
where T: PartialEq<impl Debug>
|
||||
//~^ ERROR `impl Trait` only allowed in function and inherent method argument and return types
|
||||
//~^ ERROR `impl Trait` is not allowed in bounds
|
||||
{
|
||||
}
|
||||
|
||||
// Disallowed
|
||||
fn in_Fn_parameter_in_fn_where_clause<T>()
|
||||
where T: Fn(impl Debug)
|
||||
//~^ ERROR `impl Trait` only allowed in function and inherent method argument and return types
|
||||
//~^ ERROR `impl Trait` is not allowed in the parameters of `Fn` trait bounds
|
||||
{
|
||||
}
|
||||
|
||||
// Disallowed
|
||||
fn in_Fn_return_in_fn_where_clause<T>()
|
||||
where T: Fn() -> impl Debug
|
||||
//~^ ERROR `impl Trait` only allowed in function and inherent method argument and return types
|
||||
//~^ ERROR `impl Trait` is not allowed in the return type of `Fn` trait bounds
|
||||
{
|
||||
}
|
||||
|
||||
// Disallowed
|
||||
struct InStructGenericParamDefault<T = impl Debug>(T);
|
||||
//~^ ERROR `impl Trait` only allowed in function and inherent method argument and return types
|
||||
//~^ ERROR `impl Trait` is not allowed in generic parameter defaults
|
||||
|
||||
// Disallowed
|
||||
enum InEnumGenericParamDefault<T = impl Debug> { Variant(T) }
|
||||
//~^ ERROR `impl Trait` only allowed in function and inherent method argument and return types
|
||||
//~^ ERROR `impl Trait` is not allowed in generic parameter defaults
|
||||
|
||||
// Disallowed
|
||||
trait InTraitGenericParamDefault<T = impl Debug> {}
|
||||
//~^ ERROR `impl Trait` only allowed in function and inherent method argument and return types
|
||||
//~^ ERROR `impl Trait` is not allowed in generic parameter defaults
|
||||
|
||||
// Disallowed
|
||||
type InTypeAliasGenericParamDefault<T = impl Debug> = T;
|
||||
//~^ ERROR `impl Trait` only allowed in function and inherent method argument and return types
|
||||
//~^ ERROR `impl Trait` is not allowed in generic parameter defaults
|
||||
|
||||
// Disallowed
|
||||
impl <T = impl Debug> T {}
|
||||
//~^ ERROR defaults for type parameters are only allowed in `struct`, `enum`, `type`, or `trait` definitions
|
||||
//~| WARNING this was previously accepted by the compiler but is being phased out
|
||||
//~| ERROR `impl Trait` only allowed in function and inherent method argument and return types
|
||||
//~| ERROR `impl Trait` is not allowed in generic parameter defaults
|
||||
//~| ERROR no nominal type found
|
||||
|
||||
// Disallowed
|
||||
fn in_method_generic_param_default<T = impl Debug>(_: T) {}
|
||||
//~^ ERROR defaults for type parameters are only allowed in `struct`, `enum`, `type`, or `trait` definitions
|
||||
//~| WARNING this was previously accepted by the compiler but is being phased out
|
||||
//~| ERROR `impl Trait` only allowed in function and inherent method argument and return types
|
||||
//~| ERROR `impl Trait` is not allowed in generic parameter defaults
|
||||
|
||||
fn main() {
|
||||
let _in_local_variable: impl Fn() = || {};
|
||||
//~^ ERROR `impl Trait` only allowed in function and inherent method argument and return types
|
||||
//~^ ERROR `impl Trait` is not allowed in the type of variable bindings
|
||||
let _in_return_in_local_variable = || -> impl Fn() { || {} };
|
||||
//~^ ERROR `impl Trait` only allowed in function and inherent method argument and return types
|
||||
//~^ ERROR `impl Trait` is not allowed in closure return types
|
||||
}
|
||||
|
||||
@@ -43,227 +43,301 @@ LL | type InReturnInTypeAlias<R> = fn() -> impl Debug;
|
||||
= note: see issue #63063 <https://github.com/rust-lang/rust/issues/63063> for more information
|
||||
= help: add `#![feature(type_alias_impl_trait)]` to the crate attributes to enable
|
||||
|
||||
error[E0562]: `impl Trait` only allowed in function and inherent method argument and return types, not in `fn` pointer params
|
||||
error[E0562]: `impl Trait` is not allowed in `fn` pointer parameters
|
||||
--> $DIR/where-allowed.rs:18:40
|
||||
|
|
||||
LL | fn in_fn_parameter_in_parameters(_: fn(impl Debug)) { panic!() }
|
||||
| ^^^^^^^^^^
|
||||
|
|
||||
= note: `impl Trait` is only allowed in arguments and return types of functions and methods
|
||||
|
||||
error[E0562]: `impl Trait` only allowed in function and inherent method argument and return types, not in `fn` pointer return types
|
||||
error[E0562]: `impl Trait` is not allowed in `fn` pointer return types
|
||||
--> $DIR/where-allowed.rs:22:42
|
||||
|
|
||||
LL | fn in_fn_return_in_parameters(_: fn() -> impl Debug) { panic!() }
|
||||
| ^^^^^^^^^^
|
||||
|
|
||||
= note: `impl Trait` is only allowed in arguments and return types of functions and methods
|
||||
|
||||
error[E0562]: `impl Trait` only allowed in function and inherent method argument and return types, not in `fn` pointer params
|
||||
error[E0562]: `impl Trait` is not allowed in `fn` pointer parameters
|
||||
--> $DIR/where-allowed.rs:26:38
|
||||
|
|
||||
LL | fn in_fn_parameter_in_return() -> fn(impl Debug) { panic!() }
|
||||
| ^^^^^^^^^^
|
||||
|
|
||||
= note: `impl Trait` is only allowed in arguments and return types of functions and methods
|
||||
|
||||
error[E0562]: `impl Trait` only allowed in function and inherent method argument and return types, not in `fn` pointer return types
|
||||
error[E0562]: `impl Trait` is not allowed in `fn` pointer return types
|
||||
--> $DIR/where-allowed.rs:30:40
|
||||
|
|
||||
LL | fn in_fn_return_in_return() -> fn() -> impl Debug { panic!() }
|
||||
| ^^^^^^^^^^
|
||||
|
|
||||
= note: `impl Trait` is only allowed in arguments and return types of functions and methods
|
||||
|
||||
error[E0562]: `impl Trait` only allowed in function and inherent method argument and return types, not in `Fn` trait params
|
||||
error[E0562]: `impl Trait` is not allowed in the parameters of `Fn` trait bounds
|
||||
--> $DIR/where-allowed.rs:34:49
|
||||
|
|
||||
LL | fn in_dyn_Fn_parameter_in_parameters(_: &dyn Fn(impl Debug)) { panic!() }
|
||||
| ^^^^^^^^^^
|
||||
|
|
||||
= note: `impl Trait` is only allowed in arguments and return types of functions and methods
|
||||
|
||||
error[E0562]: `impl Trait` only allowed in function and inherent method argument and return types, not in `Fn` trait return types
|
||||
error[E0562]: `impl Trait` is not allowed in the return type of `Fn` trait bounds
|
||||
--> $DIR/where-allowed.rs:38:51
|
||||
|
|
||||
LL | fn in_dyn_Fn_return_in_parameters(_: &dyn Fn() -> impl Debug) { panic!() }
|
||||
| ^^^^^^^^^^
|
||||
|
|
||||
= note: `impl Trait` is only allowed in arguments and return types of functions and methods
|
||||
|
||||
error[E0562]: `impl Trait` only allowed in function and inherent method argument and return types, not in `Fn` trait params
|
||||
error[E0562]: `impl Trait` is not allowed in the parameters of `Fn` trait bounds
|
||||
--> $DIR/where-allowed.rs:42:55
|
||||
|
|
||||
LL | fn in_dyn_Fn_parameter_in_return() -> &'static dyn Fn(impl Debug) { panic!() }
|
||||
| ^^^^^^^^^^
|
||||
|
|
||||
= note: `impl Trait` is only allowed in arguments and return types of functions and methods
|
||||
|
||||
error[E0562]: `impl Trait` only allowed in function and inherent method argument and return types, not in `Fn` trait params
|
||||
error[E0562]: `impl Trait` is not allowed in the parameters of `Fn` trait bounds
|
||||
--> $DIR/where-allowed.rs:49:51
|
||||
|
|
||||
LL | fn in_impl_Fn_parameter_in_parameters(_: &impl Fn(impl Debug)) { panic!() }
|
||||
| ^^^^^^^^^^
|
||||
|
|
||||
= note: `impl Trait` is only allowed in arguments and return types of functions and methods
|
||||
|
||||
error[E0562]: `impl Trait` only allowed in function and inherent method argument and return types, not in `Fn` trait return types
|
||||
error[E0562]: `impl Trait` is not allowed in the return type of `Fn` trait bounds
|
||||
--> $DIR/where-allowed.rs:54:53
|
||||
|
|
||||
LL | fn in_impl_Fn_return_in_parameters(_: &impl Fn() -> impl Debug) { panic!() }
|
||||
| ^^^^^^^^^^
|
||||
|
|
||||
= note: `impl Trait` is only allowed in arguments and return types of functions and methods
|
||||
|
||||
error[E0562]: `impl Trait` only allowed in function and inherent method argument and return types, not in `Fn` trait params
|
||||
error[E0562]: `impl Trait` is not allowed in the parameters of `Fn` trait bounds
|
||||
--> $DIR/where-allowed.rs:58:57
|
||||
|
|
||||
LL | fn in_impl_Fn_parameter_in_return() -> &'static impl Fn(impl Debug) { panic!() }
|
||||
| ^^^^^^^^^^
|
||||
|
|
||||
= note: `impl Trait` is only allowed in arguments and return types of functions and methods
|
||||
|
||||
error[E0562]: `impl Trait` only allowed in function and inherent method argument and return types, not in `Fn` trait params
|
||||
error[E0562]: `impl Trait` is not allowed in the parameters of `Fn` trait bounds
|
||||
--> $DIR/where-allowed.rs:66:38
|
||||
|
|
||||
LL | fn in_Fn_parameter_in_generics<F: Fn(impl Debug)> (_: F) { panic!() }
|
||||
| ^^^^^^^^^^
|
||||
|
|
||||
= note: `impl Trait` is only allowed in arguments and return types of functions and methods
|
||||
|
||||
error[E0562]: `impl Trait` only allowed in function and inherent method argument and return types, not in `Fn` trait return types
|
||||
error[E0562]: `impl Trait` is not allowed in the return type of `Fn` trait bounds
|
||||
--> $DIR/where-allowed.rs:70:40
|
||||
|
|
||||
LL | fn in_Fn_return_in_generics<F: Fn() -> impl Debug> (_: F) { panic!() }
|
||||
| ^^^^^^^^^^
|
||||
|
|
||||
= note: `impl Trait` is only allowed in arguments and return types of functions and methods
|
||||
|
||||
error[E0562]: `impl Trait` only allowed in function and inherent method argument and return types, not in field types
|
||||
error[E0562]: `impl Trait` is not allowed in field types
|
||||
--> $DIR/where-allowed.rs:83:32
|
||||
|
|
||||
LL | struct InBraceStructField { x: impl Debug }
|
||||
| ^^^^^^^^^^
|
||||
|
|
||||
= note: `impl Trait` is only allowed in arguments and return types of functions and methods
|
||||
|
||||
error[E0562]: `impl Trait` only allowed in function and inherent method argument and return types, not in field types
|
||||
error[E0562]: `impl Trait` is not allowed in field types
|
||||
--> $DIR/where-allowed.rs:87:41
|
||||
|
|
||||
LL | struct InAdtInBraceStructField { x: Vec<impl Debug> }
|
||||
| ^^^^^^^^^^
|
||||
|
|
||||
= note: `impl Trait` is only allowed in arguments and return types of functions and methods
|
||||
|
||||
error[E0562]: `impl Trait` only allowed in function and inherent method argument and return types, not in field types
|
||||
error[E0562]: `impl Trait` is not allowed in field types
|
||||
--> $DIR/where-allowed.rs:91:27
|
||||
|
|
||||
LL | struct InTupleStructField(impl Debug);
|
||||
| ^^^^^^^^^^
|
||||
|
|
||||
= note: `impl Trait` is only allowed in arguments and return types of functions and methods
|
||||
|
||||
error[E0562]: `impl Trait` only allowed in function and inherent method argument and return types, not in field types
|
||||
error[E0562]: `impl Trait` is not allowed in field types
|
||||
--> $DIR/where-allowed.rs:96:25
|
||||
|
|
||||
LL | InBraceVariant { x: impl Debug },
|
||||
| ^^^^^^^^^^
|
||||
|
|
||||
= note: `impl Trait` is only allowed in arguments and return types of functions and methods
|
||||
|
||||
error[E0562]: `impl Trait` only allowed in function and inherent method argument and return types, not in field types
|
||||
error[E0562]: `impl Trait` is not allowed in field types
|
||||
--> $DIR/where-allowed.rs:98:20
|
||||
|
|
||||
LL | InTupleVariant(impl Debug),
|
||||
| ^^^^^^^^^^
|
||||
|
|
||||
= note: `impl Trait` is only allowed in arguments and return types of functions and methods
|
||||
|
||||
error[E0562]: `impl Trait` only allowed in function and inherent method argument and return types, not in `extern fn` params
|
||||
error[E0562]: `impl Trait` is not allowed in `extern fn` parameters
|
||||
--> $DIR/where-allowed.rs:138:33
|
||||
|
|
||||
LL | fn in_foreign_parameters(_: impl Debug);
|
||||
| ^^^^^^^^^^
|
||||
|
|
||||
= note: `impl Trait` is only allowed in arguments and return types of functions and methods
|
||||
|
||||
error[E0562]: `impl Trait` only allowed in function and inherent method argument and return types, not in `extern fn` return types
|
||||
error[E0562]: `impl Trait` is not allowed in `extern fn` return types
|
||||
--> $DIR/where-allowed.rs:141:31
|
||||
|
|
||||
LL | fn in_foreign_return() -> impl Debug;
|
||||
| ^^^^^^^^^^
|
||||
|
|
||||
= note: `impl Trait` is only allowed in arguments and return types of functions and methods
|
||||
|
||||
error[E0562]: `impl Trait` only allowed in function and inherent method argument and return types, not in `fn` pointer return types
|
||||
error[E0562]: `impl Trait` is not allowed in `fn` pointer return types
|
||||
--> $DIR/where-allowed.rs:157:39
|
||||
|
|
||||
LL | type InReturnInTypeAlias<R> = fn() -> impl Debug;
|
||||
| ^^^^^^^^^^
|
||||
|
|
||||
= note: `impl Trait` is only allowed in arguments and return types of functions and methods
|
||||
|
||||
error[E0562]: `impl Trait` only allowed in function and inherent method argument and return types, not in traits
|
||||
error[E0562]: `impl Trait` is not allowed in traits
|
||||
--> $DIR/where-allowed.rs:162:16
|
||||
|
|
||||
LL | impl PartialEq<impl Debug> for () {
|
||||
| ^^^^^^^^^^
|
||||
|
|
||||
= note: `impl Trait` is only allowed in arguments and return types of functions and methods
|
||||
|
||||
error[E0562]: `impl Trait` only allowed in function and inherent method argument and return types, not in impl headers
|
||||
error[E0562]: `impl Trait` is not allowed in impl headers
|
||||
--> $DIR/where-allowed.rs:167:24
|
||||
|
|
||||
LL | impl PartialEq<()> for impl Debug {
|
||||
| ^^^^^^^^^^
|
||||
|
|
||||
= note: `impl Trait` is only allowed in arguments and return types of functions and methods
|
||||
|
||||
error[E0562]: `impl Trait` only allowed in function and inherent method argument and return types, not in impl headers
|
||||
error[E0562]: `impl Trait` is not allowed in impl headers
|
||||
--> $DIR/where-allowed.rs:172:6
|
||||
|
|
||||
LL | impl impl Debug {
|
||||
| ^^^^^^^^^^
|
||||
|
|
||||
= note: `impl Trait` is only allowed in arguments and return types of functions and methods
|
||||
|
||||
error[E0562]: `impl Trait` only allowed in function and inherent method argument and return types, not in impl headers
|
||||
error[E0562]: `impl Trait` is not allowed in impl headers
|
||||
--> $DIR/where-allowed.rs:178:24
|
||||
|
|
||||
LL | impl InInherentImplAdt<impl Debug> {
|
||||
| ^^^^^^^^^^
|
||||
|
|
||||
= note: `impl Trait` is only allowed in arguments and return types of functions and methods
|
||||
|
||||
error[E0562]: `impl Trait` only allowed in function and inherent method argument and return types, not in bounds
|
||||
error[E0562]: `impl Trait` is not allowed in bounds
|
||||
--> $DIR/where-allowed.rs:184:11
|
||||
|
|
||||
LL | where impl Debug: Debug
|
||||
| ^^^^^^^^^^
|
||||
|
|
||||
= note: `impl Trait` is only allowed in arguments and return types of functions and methods
|
||||
|
||||
error[E0562]: `impl Trait` only allowed in function and inherent method argument and return types, not in bounds
|
||||
error[E0562]: `impl Trait` is not allowed in bounds
|
||||
--> $DIR/where-allowed.rs:191:15
|
||||
|
|
||||
LL | where Vec<impl Debug>: Debug
|
||||
| ^^^^^^^^^^
|
||||
|
|
||||
= note: `impl Trait` is only allowed in arguments and return types of functions and methods
|
||||
|
||||
error[E0562]: `impl Trait` only allowed in function and inherent method argument and return types, not in bounds
|
||||
error[E0562]: `impl Trait` is not allowed in bounds
|
||||
--> $DIR/where-allowed.rs:198:24
|
||||
|
|
||||
LL | where T: PartialEq<impl Debug>
|
||||
| ^^^^^^^^^^
|
||||
|
|
||||
= note: `impl Trait` is only allowed in arguments and return types of functions and methods
|
||||
|
||||
error[E0562]: `impl Trait` only allowed in function and inherent method argument and return types, not in `Fn` trait params
|
||||
error[E0562]: `impl Trait` is not allowed in the parameters of `Fn` trait bounds
|
||||
--> $DIR/where-allowed.rs:205:17
|
||||
|
|
||||
LL | where T: Fn(impl Debug)
|
||||
| ^^^^^^^^^^
|
||||
|
|
||||
= note: `impl Trait` is only allowed in arguments and return types of functions and methods
|
||||
|
||||
error[E0562]: `impl Trait` only allowed in function and inherent method argument and return types, not in `Fn` trait return types
|
||||
error[E0562]: `impl Trait` is not allowed in the return type of `Fn` trait bounds
|
||||
--> $DIR/where-allowed.rs:212:22
|
||||
|
|
||||
LL | where T: Fn() -> impl Debug
|
||||
| ^^^^^^^^^^
|
||||
|
|
||||
= note: `impl Trait` is only allowed in arguments and return types of functions and methods
|
||||
|
||||
error[E0562]: `impl Trait` only allowed in function and inherent method argument and return types, not in generic parameter defaults
|
||||
error[E0562]: `impl Trait` is not allowed in generic parameter defaults
|
||||
--> $DIR/where-allowed.rs:218:40
|
||||
|
|
||||
LL | struct InStructGenericParamDefault<T = impl Debug>(T);
|
||||
| ^^^^^^^^^^
|
||||
|
|
||||
= note: `impl Trait` is only allowed in arguments and return types of functions and methods
|
||||
|
||||
error[E0562]: `impl Trait` only allowed in function and inherent method argument and return types, not in generic parameter defaults
|
||||
error[E0562]: `impl Trait` is not allowed in generic parameter defaults
|
||||
--> $DIR/where-allowed.rs:222:36
|
||||
|
|
||||
LL | enum InEnumGenericParamDefault<T = impl Debug> { Variant(T) }
|
||||
| ^^^^^^^^^^
|
||||
|
|
||||
= note: `impl Trait` is only allowed in arguments and return types of functions and methods
|
||||
|
||||
error[E0562]: `impl Trait` only allowed in function and inherent method argument and return types, not in generic parameter defaults
|
||||
error[E0562]: `impl Trait` is not allowed in generic parameter defaults
|
||||
--> $DIR/where-allowed.rs:226:38
|
||||
|
|
||||
LL | trait InTraitGenericParamDefault<T = impl Debug> {}
|
||||
| ^^^^^^^^^^
|
||||
|
|
||||
= note: `impl Trait` is only allowed in arguments and return types of functions and methods
|
||||
|
||||
error[E0562]: `impl Trait` only allowed in function and inherent method argument and return types, not in generic parameter defaults
|
||||
error[E0562]: `impl Trait` is not allowed in generic parameter defaults
|
||||
--> $DIR/where-allowed.rs:230:41
|
||||
|
|
||||
LL | type InTypeAliasGenericParamDefault<T = impl Debug> = T;
|
||||
| ^^^^^^^^^^
|
||||
|
|
||||
= note: `impl Trait` is only allowed in arguments and return types of functions and methods
|
||||
|
||||
error[E0562]: `impl Trait` only allowed in function and inherent method argument and return types, not in generic parameter defaults
|
||||
error[E0562]: `impl Trait` is not allowed in generic parameter defaults
|
||||
--> $DIR/where-allowed.rs:234:11
|
||||
|
|
||||
LL | impl <T = impl Debug> T {}
|
||||
| ^^^^^^^^^^
|
||||
|
|
||||
= note: `impl Trait` is only allowed in arguments and return types of functions and methods
|
||||
|
||||
error[E0562]: `impl Trait` only allowed in function and inherent method argument and return types, not in generic parameter defaults
|
||||
error[E0562]: `impl Trait` is not allowed in generic parameter defaults
|
||||
--> $DIR/where-allowed.rs:241:40
|
||||
|
|
||||
LL | fn in_method_generic_param_default<T = impl Debug>(_: T) {}
|
||||
| ^^^^^^^^^^
|
||||
|
|
||||
= note: `impl Trait` is only allowed in arguments and return types of functions and methods
|
||||
|
||||
error[E0562]: `impl Trait` only allowed in function and inherent method argument and return types, not in variable bindings
|
||||
error[E0562]: `impl Trait` is not allowed in the type of variable bindings
|
||||
--> $DIR/where-allowed.rs:247:29
|
||||
|
|
||||
LL | let _in_local_variable: impl Fn() = || {};
|
||||
| ^^^^^^^^^
|
||||
|
|
||||
= note: `impl Trait` is only allowed in arguments and return types of functions and methods
|
||||
|
||||
error[E0562]: `impl Trait` only allowed in function and inherent method argument and return types, not in closure return types
|
||||
error[E0562]: `impl Trait` is not allowed in closure return types
|
||||
--> $DIR/where-allowed.rs:249:46
|
||||
|
|
||||
LL | let _in_return_in_local_variable = || -> impl Fn() { || {} };
|
||||
| ^^^^^^^^^
|
||||
|
|
||||
= note: `impl Trait` is only allowed in arguments and return types of functions and methods
|
||||
|
||||
error: defaults for type parameters are only allowed in `struct`, `enum`, `type`, or `trait` definitions
|
||||
--> $DIR/where-allowed.rs:234:7
|
||||
|
||||
@@ -7,22 +7,22 @@ trait Iterable {
|
||||
}
|
||||
|
||||
struct Container<T: Iterable<Item = impl Foo>> {
|
||||
//~^ ERROR `impl Trait` only allowed in function and inherent method argument and return types
|
||||
//~^ ERROR `impl Trait` is not allowed in generics
|
||||
field: T
|
||||
}
|
||||
|
||||
enum Enum<T: Iterable<Item = impl Foo>> {
|
||||
//~^ ERROR `impl Trait` only allowed in function and inherent method argument and return types
|
||||
//~^ ERROR `impl Trait` is not allowed in generics
|
||||
A(T),
|
||||
}
|
||||
|
||||
union Union<T: Iterable<Item = impl Foo> + Copy> {
|
||||
//~^ ERROR `impl Trait` only allowed in function and inherent method argument and return types
|
||||
//~^ ERROR `impl Trait` is not allowed in generics
|
||||
x: T,
|
||||
}
|
||||
|
||||
type Type<T: Iterable<Item = impl Foo>> = T;
|
||||
//~^ ERROR `impl Trait` only allowed in function and inherent method argument and return types
|
||||
//~^ ERROR `impl Trait` is not allowed in generics
|
||||
|
||||
fn main() {
|
||||
}
|
||||
|
||||
@@ -1,26 +1,34 @@
|
||||
error[E0562]: `impl Trait` only allowed in function and inherent method argument and return types, not in generics
|
||||
error[E0562]: `impl Trait` is not allowed in generics
|
||||
--> $DIR/issue-47715.rs:9:37
|
||||
|
|
||||
LL | struct Container<T: Iterable<Item = impl Foo>> {
|
||||
| ^^^^^^^^
|
||||
|
|
||||
= note: `impl Trait` is only allowed in arguments and return types of functions and methods
|
||||
|
||||
error[E0562]: `impl Trait` only allowed in function and inherent method argument and return types, not in generics
|
||||
error[E0562]: `impl Trait` is not allowed in generics
|
||||
--> $DIR/issue-47715.rs:14:30
|
||||
|
|
||||
LL | enum Enum<T: Iterable<Item = impl Foo>> {
|
||||
| ^^^^^^^^
|
||||
|
|
||||
= note: `impl Trait` is only allowed in arguments and return types of functions and methods
|
||||
|
||||
error[E0562]: `impl Trait` only allowed in function and inherent method argument and return types, not in generics
|
||||
error[E0562]: `impl Trait` is not allowed in generics
|
||||
--> $DIR/issue-47715.rs:19:32
|
||||
|
|
||||
LL | union Union<T: Iterable<Item = impl Foo> + Copy> {
|
||||
| ^^^^^^^^
|
||||
|
|
||||
= note: `impl Trait` is only allowed in arguments and return types of functions and methods
|
||||
|
||||
error[E0562]: `impl Trait` only allowed in function and inherent method argument and return types, not in generics
|
||||
error[E0562]: `impl Trait` is not allowed in generics
|
||||
--> $DIR/issue-47715.rs:24:30
|
||||
|
|
||||
LL | type Type<T: Iterable<Item = impl Foo>> = T;
|
||||
| ^^^^^^^^
|
||||
|
|
||||
= note: `impl Trait` is only allowed in arguments and return types of functions and methods
|
||||
|
||||
error: aborting due to 4 previous errors
|
||||
|
||||
|
||||
@@ -1,27 +1,30 @@
|
||||
error[E0277]: can't compare `impl PartialEq + Destruct + Copy` with `impl PartialEq + Destruct + Copy`
|
||||
--> $DIR/const-impl-trait.rs:28:17
|
||||
error[E0277]: can't compare `()` with `()`
|
||||
--> $DIR/const-impl-trait.rs:35:17
|
||||
|
|
||||
LL | fn huh() -> impl ~const PartialEq + ~const Destruct + Copy {
|
||||
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ no implementation for `impl PartialEq + Destruct + Copy == impl PartialEq + Destruct + Copy`
|
||||
LL | assert!(cmp(&()));
|
||||
| --- ^^^ no implementation for `() == ()`
|
||||
| |
|
||||
| required by a bound introduced by this call
|
||||
|
|
||||
= help: the trait `~const PartialEq` is not implemented for `impl PartialEq + Destruct + Copy`
|
||||
note: required by a bound in `Foo::{opaque#0}`
|
||||
--> $DIR/const-impl-trait.rs:24:22
|
||||
= help: the trait `const PartialEq` is not implemented for `()`
|
||||
= help: the trait `PartialEq` is implemented for `()`
|
||||
note: required by a bound in `cmp`
|
||||
--> $DIR/const-impl-trait.rs:12:23
|
||||
|
|
||||
LL | fn huh() -> impl ~const PartialEq + ~const Destruct + Copy;
|
||||
| ^^^^^^^^^^^^^^^^ required by this bound in `Foo::{opaque#0}`
|
||||
LL | const fn cmp(a: &impl ~const PartialEq) -> bool {
|
||||
| ^^^^^^^^^^^^^^^^ required by this bound in `cmp`
|
||||
|
||||
error[E0277]: can't drop `impl PartialEq + Destruct + Copy`
|
||||
--> $DIR/const-impl-trait.rs:28:17
|
||||
error[E0277]: can't compare `&impl ~const PartialEq` with `&impl ~const PartialEq`
|
||||
--> $DIR/const-impl-trait.rs:13:7
|
||||
|
|
||||
LL | fn huh() -> impl ~const PartialEq + ~const Destruct + Copy {
|
||||
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `~const Destruct` is not implemented for `impl PartialEq + Destruct + Copy`
|
||||
LL | a == a
|
||||
| ^^ no implementation for `&impl ~const PartialEq == &impl ~const PartialEq`
|
||||
|
|
||||
note: required by a bound in `Foo::{opaque#0}`
|
||||
--> $DIR/const-impl-trait.rs:24:41
|
||||
= help: the trait `~const PartialEq<&impl ~const PartialEq>` is not implemented for `&impl ~const PartialEq`
|
||||
help: consider dereferencing both sides of the expression
|
||||
|
|
||||
LL | fn huh() -> impl ~const PartialEq + ~const Destruct + Copy;
|
||||
| ^^^^^^^^^^^^^^^ required by this bound in `Foo::{opaque#0}`
|
||||
LL | *a == *a
|
||||
| + +
|
||||
|
||||
error: aborting due to 2 previous errors
|
||||
|
||||
|
||||
@@ -0,0 +1,29 @@
|
||||
// Regression test for issue #119700.
|
||||
// check-pass
|
||||
|
||||
#![feature(const_trait_impl, effects)]
|
||||
|
||||
#[const_trait]
|
||||
trait Main {
|
||||
fn compute<T: ~const Aux>() -> u32;
|
||||
}
|
||||
|
||||
impl const Main for () {
|
||||
fn compute<T: ~const Aux>() -> u32 {
|
||||
T::generate()
|
||||
}
|
||||
}
|
||||
|
||||
#[const_trait]
|
||||
trait Aux {
|
||||
fn generate() -> u32;
|
||||
}
|
||||
|
||||
impl const Aux for () {
|
||||
fn generate() -> u32 { 1024 }
|
||||
}
|
||||
|
||||
fn main() {
|
||||
const _: u32 = <()>::compute::<()>();
|
||||
let _ = <()>::compute::<()>();
|
||||
}
|
||||
@@ -6,7 +6,7 @@ LL | Pin::new(S).x();
|
||||
| |
|
||||
| required by a bound introduced by this call
|
||||
|
|
||||
note: required by a bound in `Pin::<P>::new`
|
||||
note: required by a bound in `Pin::<Ptr>::new`
|
||||
--> $SRC_DIR/core/src/pin.rs:LL:COL
|
||||
help: consider borrowing here
|
||||
|
|
||||
|
||||
@@ -52,7 +52,7 @@ LL | Pin::new(x)
|
||||
|
|
||||
= note: consider using the `pin!` macro
|
||||
consider using `Box::pin` if you need to access the pinned value outside of the current scope
|
||||
note: required by a bound in `Pin::<P>::new`
|
||||
note: required by a bound in `Pin::<Ptr>::new`
|
||||
--> $SRC_DIR/core/src/pin.rs:LL:COL
|
||||
|
||||
error[E0277]: `dyn Future<Output = i32> + Send` cannot be unpinned
|
||||
@@ -65,7 +65,7 @@ LL | Pin::new(Box::new(x))
|
||||
|
|
||||
= note: consider using the `pin!` macro
|
||||
consider using `Box::pin` if you need to access the pinned value outside of the current scope
|
||||
note: required by a bound in `Pin::<P>::new`
|
||||
note: required by a bound in `Pin::<Ptr>::new`
|
||||
--> $SRC_DIR/core/src/pin.rs:LL:COL
|
||||
|
||||
error[E0308]: mismatched types
|
||||
|
||||
@@ -4,7 +4,7 @@
|
||||
// FIXME: this is ruled out for now but should work
|
||||
|
||||
type Foo = fn() -> impl Send;
|
||||
//~^ ERROR: `impl Trait` only allowed in function and inherent method argument and return types
|
||||
//~^ ERROR: `impl Trait` is not allowed in `fn` pointer return types
|
||||
|
||||
fn make_foo() -> Foo {
|
||||
|| 15
|
||||
|
||||
@@ -1,8 +1,10 @@
|
||||
error[E0562]: `impl Trait` only allowed in function and inherent method argument and return types, not in `fn` pointer return types
|
||||
error[E0562]: `impl Trait` is not allowed in `fn` pointer return types
|
||||
--> $DIR/type-alias-impl-trait-fn-type.rs:6:20
|
||||
|
|
||||
LL | type Foo = fn() -> impl Send;
|
||||
| ^^^^^^^^^
|
||||
|
|
||||
= note: `impl Trait` is only allowed in arguments and return types of functions and methods
|
||||
|
||||
error: aborting due to 1 previous error
|
||||
|
||||
|
||||
@@ -1,6 +1,6 @@
|
||||
struct S;
|
||||
fn f() {
|
||||
let _: S<impl Oops> = S; //~ ERROR cannot find trait `Oops` in this scope
|
||||
//~^ ERROR `impl Trait` only allowed in function and inherent method argument and return types
|
||||
//~^ ERROR `impl Trait` is not allowed in the type of variable bindings
|
||||
}
|
||||
fn main() {}
|
||||
|
||||
@@ -4,11 +4,13 @@ error[E0405]: cannot find trait `Oops` in this scope
|
||||
LL | let _: S<impl Oops> = S;
|
||||
| ^^^^ not found in this scope
|
||||
|
||||
error[E0562]: `impl Trait` only allowed in function and inherent method argument and return types, not in variable bindings
|
||||
error[E0562]: `impl Trait` is not allowed in the type of variable bindings
|
||||
--> $DIR/issue-104513-ice.rs:3:14
|
||||
|
|
||||
LL | let _: S<impl Oops> = S;
|
||||
| ^^^^^^^^^
|
||||
|
|
||||
= note: `impl Trait` is only allowed in arguments and return types of functions and methods
|
||||
|
||||
error: aborting due to 2 previous errors
|
||||
|
||||
|
||||
@@ -1,7 +0,0 @@
|
||||
# Everyone uses make for building Rust
|
||||
|
||||
foo: bar.rlib
|
||||
$(RUSTC) --crate-type bin --extern bar=bar.rlib
|
||||
|
||||
%.rlib: %.rs
|
||||
$(RUSTC) --crate-type lib $<
|
||||
Reference in New Issue
Block a user